CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid in Capital	Retained Earnings (Accumulated Deficit)
Balance at Dec. 31, 2017	$ 376,209	$ 1,136	$ 546,766	$ (171,693)
Balance, shares at Dec. 31, 2017		113,572
Vesting of restricted stock units		$ 7	(7)
Vesting of restricted stock units, shares		766
Stock compensation expense	2,890		2,890
Exercise of stock options	2,041	$ 5	2,036
Exercise of stock options, shares		517
Repurchase of common stock	(4,855)	$ (2)	(4,853)
Repurchase of common stock, shares		(236)
Cumulative effect adjustment	1,468			1,468
Net income	23,220			23,220
Balance at Mar. 31, 2018	400,973	$ 1,146	546,832	(147,005)
Balance, shares at Mar. 31, 2018		114,619
Balance at Dec. 31, 2018	$ 596,338	$ 1,151	560,221	34,966
Balance, shares at Dec. 31, 2018	115,078	115,078
Vesting of restricted stock units		$ 7	(7)
Vesting of restricted stock units, shares		662
Stock compensation expense	$ 2,659		2,659
Exercise of stock options	216		216
Exercise of stock options, shares		59
Repurchase of common stock	(2,450)	$ (2)	(2,448)
Repurchase of common stock, shares		(196)
Net income	35,708			35,708
Balance at Mar. 31, 2019	$ 632,471	$ 1,156	$ 560,641	$ 70,674
Balance, shares at Mar. 31, 2019	115,603	115,603