CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Balance at period start (in shares) at Dec. 31, 2017		45,776
Balance at period start at Dec. 31, 2017	$ 447,719	$ 458	$ 593,295	$ (148,178)	$ 2,144
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)		272
Stock-based compensation	1,438	$ 1	1,437
Purchase of common stock for retirement (in shares)		(29)
Purchase of common stock for retirement	(543)		(543)
Net income	15,185			15,185
Balance at period end (in shares) at Mar. 31, 2018		46,019
Balance at period end at Mar. 31, 2018	463,799	$ 459	594,189	(132,993)	2,144
Balance at period start (in shares) at Dec. 31, 2018		46,984
Balance at period start at Dec. 31, 2018	512,329	$ 470	617,937	(108,751)	2,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)		2,364
Issuance of common stock	36,980	$ 23	36,957
Stock-based compensation (in shares)		246
Stock-based compensation	1,535	$ 3	1,532
Purchase of common stock for retirement (in shares)		(44)
Purchase of common stock for retirement	(734)		(734)
Net income	61,092			61,092
Balance at period end (in shares) at Mar. 31, 2019		49,550
Balance at period end at Mar. 31, 2019	$ 611,202	$ 496	$ 655,692	$ (47,659)	$ 2,673