Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Total
Beginning balance at Dec. 31, 2017	$ 295	$ 566,790	$ 168,148	$ 735,233
Beginning balance (in shares) at Dec. 31, 2017	29,503
Issuance of common stock, net	$ 11	31,219		31,230
Issuance of common stock, net, shares	1,086
Vesting of restricted stock units	$ 2	(5,483)		(5,481)
Vesting of restricted stock units, shares	170
Stock-based compensation expense		10,133		10,133
Net income			70,261	70,261
Ending balance at Sep. 30, 2018	$ 308	602,659	237,826	840,793
Ending balance (in shares) at Sep. 30, 2018	30,759
Beginning balance at Jun. 30, 2018	$ 301	582,627	220,778	803,706
Beginning balance (in shares) at Jun. 30, 2018	30,119
Issuance of common stock, net	$ 6	16,915		16,921
Issuance of common stock, net, shares	600
Vesting of restricted stock units	$ 1	(695)		(694)
Vesting of restricted stock units, shares	40
Stock-based compensation expense		3,812		3,812
Net income			17,048	17,048
Ending balance at Sep. 30, 2018	$ 308	602,659	237,826	840,793
Ending balance (in shares) at Sep. 30, 2018	30,759
Adoption of ASC 606			(583)	(583)
Beginning balance at Dec. 31, 2018	$ 302	595,037	264,020	859,359
Beginning balance (in shares) at Dec. 31, 2018	30,155
Issuance of common stock, net	$ 9	25,808		25,817
Issuance of common stock, net, shares	899
Repurchase of common stock	$ (1)	(1,438)		(1,439)
Repurchase of common stock, shares	(83)
Vesting of restricted stock units	$ 2	(3,587)		(3,585)
Vesting of restricted stock units, shares	278
Stock-based compensation expense		11,391		11,391
Net income			59,636	59,636
Ending balance at Sep. 30, 2019	$ 312	627,211	323,656	951,179
Ending balance (in shares) at Sep. 30, 2019	31,249
Beginning balance at Jun. 30, 2019	$ 304	600,293	296,632	897,229
Beginning balance (in shares) at Jun. 30, 2019	30,439
Issuance of common stock, net	$ 8	23,146		23,154
Issuance of common stock, net, shares	799
Vesting of restricted stock units		(151)		(151)
Vesting of restricted stock units, shares	11
Stock-based compensation expense		3,923		3,923
Net income			27,024	27,024
Ending balance at Sep. 30, 2019	$ 312	$ 627,211	$ 323,656	$ 951,179
Ending balance (in shares) at Sep. 30, 2019	31,249