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)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 30, 2017	$ 321,809	$ 279	$ 128,419	$ 222,974	$ (22,539)	$ (7,324)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,356			8,356
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)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Jun. 30, 2018	318,843	279	132,198	211,494	(17,717)	(7,411)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,237			6,237
Other comprehensive income (loss)	(668)					(668)
Open market purchases of treasury shares	(5,190)				(5,190)
Treasury shares sold to Employee Stock Purchase Plan	153		19		134
Exercise of stock options	128		(126)		254
Issuance of deferred shares	0		(5,940)		5,940
Other treasury share purchases	(1,651)				(1,651)
Stock-based compensation expense	5,738		5,738
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2018	$ 323,590	$ 279	$ 131,889	$ 217,731	$ (18,230)	$ (8,079)