Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Dec. 31, 2015	$ 310,835	$ 3,353	$ 131,980	$ 245,698	$ (14,747)	$ (55,449)
Balance (in shares) at Dec. 31, 2015		33,528,915
Net income	81,678			81,678
Other comprehensive income (loss)	(10,071)					(10,071)
Exercise of stock options	4,941	$ 40	4,901
Exercise of stock options (in shares)		398,680
Vested restricted stock			(92)		92
Vested performance shares			(1,152)		1,152
Stock option expense	3,816		3,816
Restricted stock expense	489		489
Performance stock expense (benefit)	3,461		3,461
Excess tax benefits	10,278		10,278
Balance at Dec. 31, 2016	405,427	$ 3,393	153,681	327,376	(13,503)	(65,520)
Balance (in shares) at Dec. 31, 2016		33,927,595
Net income	102,450			102,450
Other comprehensive income (loss)	23,292					23,292
Exercise of stock options	4,781	$ 34	4,747
Exercise of stock options (in shares)		343,380
Vested restricted stock			(83)		83
Vested performance shares			(1,280)		1,280
Stock option expense	4,368		4,368
Restricted stock expense	571		571
Performance stock expense (benefit)	3,975		3,975
Balance at Dec. 31, 2017	$ 544,864	$ 3,427	165,979	429,826	(12,140)	(42,228)
Balance (in shares) at Dec. 31, 2017	34,270,975	34,270,975
Impact of change in accounting policy	$ 16,219			16,219
Adjusted balance at January 1, 2018	561,083	$ 3,427	165,979	446,045	(12,140)	(42,228)
Net income	92,418			92,418
Other comprehensive income (loss)	(17,909)					(17,909)
Exercise of stock options	14,041	$ 60	13,981
Exercise of stock options (in shares)		599,149
Vested restricted stock			(85)		85
Vested performance shares			(1,278)		1,278
Stock option expense	4,288		4,288
Restricted stock expense	533		533
Performance stock expense (benefit)	(727)		(727)
Balance at Dec. 31, 2018	$ 653,727	$ 3,487	$ 182,691	$ 538,463	$ (10,777)	$ (60,137)
Balance (in shares) at Dec. 31, 2018	34,870,124	34,870,124