Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid In Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2017			34,185,163
Beginning balance at Dec. 31, 2017	$ 950,438		$ 340	$ 520,304	$ 431,544		$ (1,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	152,276				152,276
OCI, before reclassifications, net of tax	(1,851)						(1,851)
Other comprehensive income, net of tax	(2,525)
Stock-based compensation expense	6,494			6,494
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)			108,201
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes	776		$ 1	775
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)			(14,162)
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes			$ 1	(1)
Time based stock awards granted (in shares)			94,344
Issuance of common stock related to employee stock purchase plan (in shares)			14,373
Issuance of common stock related to employee stock purchase plan	808		$ 0	808	0
Ending balance (in shares) at Dec. 31, 2018			34,387,919
Ending balance at Dec. 31, 2018	1,108,941		$ 342	528,380	584,494	$ 674	(4,275)	$ (674)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	142,943				142,943
Other comprehensive income, net of tax	7,234						7,234
Stock-based compensation expense	7,684			7,684
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)			26,784
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes	332		$ 0	332
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)			(15,127)
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes			$ 1	(1)
Vesting of performance based stock awards, net of shares withheld for payroll taxes (in shares)			17,655
Time based stock awards granted (in shares)			112,636
Issuance of common stock related to employee stock purchase plan (in shares)			16,129
Issuance of common stock related to employee stock purchase plan	782			782
Cash dividends declared	(22,332)				(22,332)
Common stock repurchased (in shares)			(1,304,500)
Common stock repurchased	$ (54,903)		$ (12)	(54,891)
Ending balance (in shares) at Dec. 31, 2019	33,241,496		33,241,496
Ending balance at Dec. 31, 2019	$ 1,190,681	$ (10,931)	$ 331	482,286	705,105	$ (10,931)	2,959
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	132,217				132,217
Other comprehensive income, net of tax	12,541						12,541
Stock-based compensation expense	5,324			5,324
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)			3,300
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes	63			63
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)			(28,811)
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes	(1)			(1)
Vesting of performance based stock awards, net of shares withheld for payroll taxes (in shares)			4,126
Time based stock awards granted (in shares)			176,252
Issuance of common stock related to employee stock purchase plan (in shares)			24,210
Issuance of common stock related to employee stock purchase plan	760			760
Cash dividends declared	(28,330)				(28,330)
Common stock repurchased (in shares)			(1,640,910)
Common stock repurchased	$ (61,432)		$ (16)	(61,416)
Ending balance (in shares) at Dec. 31, 2020	31,779,663		31,779,663
Ending balance at Dec. 31, 2020	$ 1,240,892		$ 315	$ 427,016	$ 798,061		$ 15,500