Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Shareholders' Equity, Stock Options and Net Income per Share - Net Income per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
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, 2018
Dec. 31, 2017
Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                      
Net income and comprehensive income $ 27,684 $ 22,329 $ 24,298 $ 17,741 $ 34,681 $ 18,328 $ 19,666 $ 14,581 $ 92,051 $ 87,255 $ 27,505
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic                 (881) (700) (210)
Numerator for net income and comprehensive income to common shareholders                 $ 91,170 $ 86,555 $ 27,295
Denominator for basic income per share - weighted-average shares                 29,076 29,867 30,283
Denominator for diluted income per share - adjusted weighted-average shares                 29,190 29,964 30,444
Basic net income per share $ 0.95 $ 0.76 $ 0.83 $ 0.60 $ 1.17 $ 0.61 $ 0.65 $ 0.48 $ 3.14 $ 2.90 $ 0.90
Diluted net income per share $ 0.95 $ 0.76 $ 0.82 $ 0.60 $ 1.16 $ 0.61 $ 0.65 $ 0.48 $ 3.12 $ 2.89 $ 0.90
Total number anti-dilutive options and non-vested shares excluded from income per diluted share computation                 151 172 310
Equity Option [Member]                      
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                      
Weighted Average Number Diluted Shares Outstanding Adjustment                 80 64 130
Total number anti-dilutive options and non-vested shares excluded from income per diluted share computation                 126 172 310
Key Employee Performance Share Based Plan [Member]                      
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                      
Weighted Average Number Diluted Shares Outstanding Adjustment                 34 33 31
Total number anti-dilutive options and non-vested shares excluded from income per diluted share computation                 16    
Employee Non-vested Shares [Member]                      
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]                      
Total number anti-dilutive options and non-vested shares excluded from income per diluted share computation                 9