Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock [Member]	Additional paid-in capital [Member]	Treasury stock [Member]	Accumulated other comprehensive income (loss) [Member]	Retained earnings [Member]
Balance (in shares) at Dec. 31, 2017		58,551,761
Balance at Dec. 31, 2017	$ 336,289	$ 59	$ 351,042	$ (239,199)	$ (642)	$ 225,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,751					17,751
Payment of dividends	(5,825)					(5,825)
Exercise of stock options and stock appreciation rights and vesting of restricted stock units (in shares)		279,422
Exercise of stock options and stock appreciation rights and vesting of restricted stock units	9		9
Employee taxes paid for withheld shares upon equity award settlement	(22,511)			(22,511)
Stock-based compensation	11,092		11,062			30
Restricted stock grants (in shares)		437,878
Restricted stock grants	0	$ 0
Restricted stock cancellations (in shares)		(35,218)
Other comprehensive income	7,516				7,516
Reclassification upon early adoption of ASU 2018-02	0				167	(167)
Balance (in shares) at Mar. 31, 2018		59,233,843
Balance at Mar. 31, 2018	344,321	$ 59	362,113	(261,710)	7,041	236,818
Balance (in shares) at Dec. 31, 2017		58,551,761
Balance at Dec. 31, 2017	336,289	$ 59	351,042	(239,199)	(642)	225,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,343
Balance (in shares) at Jun. 30, 2018		59,301,209
Balance at Jun. 30, 2018	348,223	$ 59	375,949	(264,383)	(1,011)	237,609
Balance (in shares) at Mar. 31, 2018		59,233,843
Balance at Mar. 31, 2018	344,321	$ 59	362,113	(261,710)	7,041	236,818
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,592					6,592
Payment of dividends	(5,828)					(5,828)
Exercise of stock options and stock appreciation rights and vesting of restricted stock units (in shares)		40,741
Exercise of stock options and stock appreciation rights and vesting of restricted stock units	2		2
Employee taxes paid for withheld shares upon equity award settlement	(2,673)			(2,673)
Stock-based compensation	13,861		13,834			27
Restricted stock grants (in shares)		68,313
Restricted stock grants	0	$ 0
Restricted stock cancellations (in shares)		41,688
Other comprehensive income	(8,052)				(8,052)
Balance (in shares) at Jun. 30, 2018		59,301,209
Balance at Jun. 30, 2018	348,223	$ 59	375,949	(264,383)	(1,011)	237,609
Balance (in shares) at Dec. 31, 2018		59,327,633
Balance at Dec. 31, 2018	373,783	$ 59	399,241	(266,884)	(5,110)	246,477
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	(1,122)					(1,122)
Payment of dividends	(5,901)					(5,901)
Exercise of stock options and stock appreciation rights and vesting of restricted stock units (in shares)		234,453
Exercise of stock options and stock appreciation rights and vesting of restricted stock units	3		3
Employee taxes paid for withheld shares upon equity award settlement	(18,400)			(18,400)
Stock-based compensation	13,726		13,693			33
Restricted stock grants (in shares)		663,906
Restricted stock grants	1	$ 1
Restricted stock cancellations (in shares)		(43,314)
Other comprehensive income	3,658				3,658
Balance (in shares) at Mar. 31, 2019		60,182,678
Balance at Mar. 31, 2019	365,748	$ 60	412,937	(285,284)	(1,452)	239,487
Balance (in shares) at Dec. 31, 2018		59,327,633
Balance at Dec. 31, 2018	373,783	$ 59	399,241	(266,884)	(5,110)	246,477
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,018
Balance (in shares) at Jun. 30, 2019		60,187,063
Balance at Jun. 30, 2019	372,702	$ 60	427,950	(286,644)	(9,409)	240,745
Balance (in shares) at Mar. 31, 2019		60,182,678
Balance at Mar. 31, 2019	365,748	$ 60	412,937	(285,284)	(1,452)	239,487
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,140					7,140
Payment of dividends	(5,901)					(5,901)
Exercise of stock options and stock appreciation rights and vesting of restricted stock units (in shares)		21,726
Exercise of stock options and stock appreciation rights and vesting of restricted stock units	3		3
Employee taxes paid for withheld shares upon equity award settlement	(1,360)			(1,360)
Stock-based compensation	15,029		15,010			19
Restricted stock grants (in shares)		12,405
Restricted stock grants	0	$ 0
Restricted stock cancellations (in shares)		29,746
Other comprehensive income	(7,957)				(7,957)
Balance (in shares) at Jun. 30, 2019		60,187,063
Balance at Jun. 30, 2019	$ 372,702	$ 60	$ 427,950	$ (286,644)	$ (9,409)	$ 240,745