Annual report pursuant to Section 13 and 15(d)

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

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Shareholders' Equity, Stock Options and Net Income per Share - Common and Preferred Stock (Details) - USD ($)
$ / shares in Units, $ in Thousands
 2 Months Ended 3 Months Ended 12 Months Ended
Feb. 19, 2014
Mar. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2008
May. 31, 2008
Preferred Stock [Abstract]              
Preferred stock, shares authorized     5,000,000 5,000,000      
Preferred stock par value per share     $ 0.01 $ 0.01      
Cash Dividends [Abstract]              
Quarterly cash dividend per share, common stock   $ 0.12 $ 0.12 $ 0.12 $ 0.10    
Repurchase of Common Stock [Abstract]              
Repurchase of common stock (repurchase program)     $ 19,992 $ 39,972 $ 354    
Common Stock [Member]              
Repurchase of Common Stock [Abstract]              
Share repurchase program, authorized shares 2,000,000   2,000,000        
Stock Repurchased During Period, Shares     422,404 881,979 8,675    
Repurchase of common stock (repurchase program)     $ 19,992 $ 39,972 $ 354    
Treasury stock acquired, average cost per share     $ 47.33 $ 45.32 $ 40.84    
Remaining shares authorized under share repurchase program     695,617        
Share-based Compensation [Abstract]              
Number of shares authorized under the plan     7,500,000     4,500,000  
Additional authorized shares for employee stock awards     537,400       3,000,000
Minimum [Member] | Employee Stock Option [Member]              
Share-based Compensation [Abstract]              
Expected life of options (in years)     7 years        
Option award vesting period     1 year        
Maximum [Member] | Employee Stock Option [Member]              
Share-based Compensation [Abstract]              
Expected life of options (in years)     10 years        
Option award vesting period     5 years