Consolidated Statement of Shareholders' Equity (Unaudited) - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2017	96,536,251			13,279,393
Balance at Dec. 31, 2017	$ 965	$ 368,721	$ 366,164	$ (129,621)	$ 606,229
Adoption of accounting standard (Note 1 and 3) (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2017			1,427		1,427
Net income			3,024		3,024
Stock-based compensation expense		14,208			14,208
Purchase of treasury stock (in shares)				383,801
Purchase of treasury stock				$ (5,955)	$ (5,955)
Exercise of stock options (in shares)	151,034				151,034
Exercise of stock options	$ 2	2,388			$ 2,390
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)	363,823
Vesting of restricted stock units, net of shares withheld for employee tax	$ 3	(2,687)			(2,684)
Balance (in shares) at Jun. 30, 2018	97,051,108			13,663,194
Balance at Jun. 30, 2018	$ 970	$ 382,630	$ 370,615	$ (135,576)	$ 618,639