CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	AOCI Attributable to Parent
Balance at Dec. 31, 2015	$ 413,474	$ 326		$ 438,716	$ (23,009)	$ (2,559)
Net income	13,425				13,425
Foreign currency translation	(1,183)					(1,183)
Stock-based compensation expense	2,777	1		2,776
Stock options exercised	678			678
Issuance of common stock	173,578	80		173,498
Common stock issuance costs	(2,719)			(2,719)
Reclassification of liability classified stock options upon IPO	10,463			10,463
Tax effect of initial public offering related costs	192			192
Tax benefit from stock-based compensation	25			25
Balance at Dec. 31, 2016	610,710	407		623,629	(9,584)	(3,742)
Impact to Retained Earnings from adoption | ASU 2016-09				440	(440)
Balance	610,710	407		624,069	(10,024)	(3,742)
Net income	39,122				39,122
Foreign currency translation	3,008					3,008
Stock-based compensation expense	4,463			4,463
Stock options exercised	1,812	1		1,811
Repurchases of common stock	(149,551)	(51)			(149,500)
Treasury stock purchases	(6,032)	(2)	$ (6,030)
Tax effect of initial public offering related costs	(2)			(2)
Balance at Dec. 31, 2017	503,530	355	(6,030)	630,341	(120,402)	(734)
Impact to Retained Earnings from adoption | ASU 2014-09	5,730				5,730
Balance	509,260	355	(6,030)	630,341	(114,672)	(734)
Net income	73,185				73,185
Foreign currency translation	(1,783)					(1,783)
Stock-based compensation expense	6,499			6,499
Stock options exercised	2,542	1		2,541
Balance at Dec. 31, 2018	$ 589,703	$ 356	$ (6,030)	$ 639,381	$ (41,487)	$ (2,517)