CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	(Accumulated Deficit) Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Impact to Retained Earnings from adoption | ASU 2014-09	$ 5,730				$ 5,730
Balance	509,260	$ 355	$ (6,030)	$ 630,341	(114,672)	$ (734)
Balance at Dec. 31, 2017	503,530	355	(6,030)	630,341	(120,402)	(734)
Net income	14,551				14,551
Foreign currency translation	629					629
Stock-based compensation expense	1,467			1,467
Stock options exercised	566			566
Balance at Mar. 31, 2018	526,473	355	(6,030)	632,374	(100,121)	(105)
Balance at Dec. 31, 2017	503,530	355	(6,030)	630,341	(120,402)	(734)
Net income	50,424
Foreign currency translation	(1,445)
Balance at Sep. 30, 2018	564,435	356	(6,030)	636,536	(64,248)	(2,179)
Balance at Mar. 31, 2018	526,473	355	(6,030)	632,374	(100,121)	(105)
Net income	16,568				16,568
Foreign currency translation	(2,010)					(2,010)
Stock-based compensation expense	1,487			1,487
Stock options exercised	609	1		608
Balance at Jun. 30, 2018	543,127	356	(6,030)	634,469	(83,553)	(2,115)
Net income	19,305				19,305
Foreign currency translation	(64)					(64)
Stock-based compensation expense	1,432			1,432
Stock options exercised	635			635
Balance at Sep. 30, 2018	564,435	356	(6,030)	636,536	(64,248)	(2,179)
Impact to Retained Earnings from adoption | ASU 2016-02	9,153				9,153
Balance	598,856	356	(6,030)	639,381	(32,334)	(2,517)
Balance at Dec. 31, 2018	589,703	356	(6,030)	639,381	(41,487)	(2,517)
Net income	19,198				19,198
Foreign currency translation	(274)					(274)
Stock-based compensation expense	3,183			3,183
Stock options exercised	934	1		933
Balance at Mar. 31, 2019	621,897	357	(6,030)	643,497	(13,136)	(2,791)
Balance at Dec. 31, 2018	589,703	356	(6,030)	639,381	(41,487)	(2,517)
Net income	70,630
Foreign currency translation	(1,146)
Balance at Sep. 30, 2019	692,007	360	(6,030)	663,044	38,296	(3,663)
Balance at Mar. 31, 2019	621,897	357	(6,030)	643,497	(13,136)	(2,791)
Net income	27,455				27,455
Foreign currency translation	414					414
Stock-based compensation expense	5,385			5,385
Stock options exercised	2,904	2		2,902
Balance at Jun. 30, 2019	658,055	359	(6,030)	651,784	14,319	(2,377)
Net income	23,977				23,977
Foreign currency translation	(1,286)					(1,286)
Stock-based compensation expense	9,466			9,466
Stock options exercised	1,795	1		1,794
Balance at Sep. 30, 2019	$ 692,007	$ 360	$ (6,030)	$ 663,044	$ 38,296	$ (3,663)