Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning equity balances, as adjusted	$ 315,566	$ 279	$ 127,058	$ 223,157	$ (26,907)	$ (6,845)	$ (1,176)
Retrospective adjustment upon adoption of ASU 2016-09	0		100	(100)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 30, 2016	315,566	279	126,958	223,257	(26,907)	(6,845)	(1,176)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,592			14,592			0
Other comprehensive income (loss)	(1,997)					(1,997)
Treasury shares sold to Employee Stock Purchase Plan	169		12		157
Exercise of stock options	222		(273)		495
Issuance of deferred shares	0		(5,685)		5,685
Other treasury share purchases	(2,270)				(2,270)
Stock-based compensation expense	3,547		3,547
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2016	329,829	279	124,659	237,749	(22,840)	(8,842)	(1,176)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 30, 2017	321,809	279	128,419	222,974	(22,539)	(7,324)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,356			8,356			0
Other comprehensive income (loss)	1,536					1,536
Treasury shares sold to Employee Stock Purchase Plan	144		(109)		253
Issuance of deferred shares	0		(4,428)		4,428
Other treasury share purchases	(612)				(612)
Stock-based compensation expense	4,353		4,353
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2017	$ 335,586	$ 279	$ 128,235	$ 231,330	$ (18,470)	$ (5,788)	$ 0