Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity, Stock Options and Net Income per Share - Common and Preferred Stock (Details)

v3.10.0.1
Shareholders' Equity, Stock Options and Net Income per Share - Common and Preferred Stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Feb. 05, 2019
Jul. 21, 2016
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
May 31, 2016
Preferred Stock [Abstract]                                      
Preferred stock, shares authorized       5,000,000       5,000,000               5,000,000 5,000,000    
Preferred stock par value per share       $ 0.01       $ 0.01               $ 0.01 $ 0.01    
Cash Dividends [Abstract]                                      
Quarterly cash dividend per share, common stock     $ 0.18 $ 0.18 $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.15 $ 0.12 $ 0.12 $ 0.12        
Repurchase of Common Stock [Abstract]                                      
Repurchase of common stock (repurchase program)                               $ 66,126 $ 48,983 $ 39,983  
Common Stock [Member]                                      
Share-based Compensation [Abstract]                                      
Additional authorized shares for employee stock awards       1,266,219                       1,266,219     2,000,000
Employee Stock Option [Member]                                      
Share-based Compensation [Abstract]                                      
Expected life of options (in years)                               7 years      
Minimum [Member] | Employee Stock Option [Member]                                      
Share-based Compensation [Abstract]                                      
Option award vesting period                               2 years      
Maximum [Member] | Employee Stock Option [Member]                                      
Share-based Compensation [Abstract]                                      
Option award vesting period                               3 years      
2016 Stock Repurchase Plan [Member] | Common Stock [Member]                                      
Repurchase of Common Stock [Abstract]                                      
Share repurchase program, authorized shares   3,000,000                                  
Stock Repurchased During Period, Shares                               1,109,270      
Repurchase of common stock (repurchase program)                               $ 66,126      
Treasury stock acquired, average cost per share                               $ 59.61      
Remaining shares authorized under share repurchase program                               709,395      
2019 Stock Repurchase Plan [Member] | Common Stock [Member]                                      
Repurchase of Common Stock [Abstract]                                      
Share repurchase program, authorized shares 5,000,000