Summary of Significant Accounting Policies - Weighted Average Shares Outstanding for Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Earnings per share — Basic:
Net income	$ 3,928	$ 4,824	$ 13,094	$ 2,648	$ (11,047)	$ 1,541	$ 8,030	$ 3,896	$ 24,494	$ 2,420	$ 18,241
Weighted-average shares outstanding — Basic	64,749	64,637	64,265	64,019	63,888	63,706	63,513	62,636	64,417	63,435	61,818
Net income per common share — Basic	$ 0.06	$ 0.07	$ 0.20	$ 0.04	$ (0.17)	$ 0.02	$ 0.13	$ 0.06	$ 0.38	$ 0.04	$ 0.30
Earnings per share — Diluted:
Net income	$ 3,928	$ 4,824	$ 13,094	$ 2,648	$ (11,047)	$ 1,541	$ 8,030	$ 3,896	$ 24,494	$ 2,420	$ 18,241
Weighted-average shares outstanding — Basic	64,749	64,637	64,265	64,019	63,888	63,706	63,513	62,636	64,417	63,435	61,818
Effect of potentially dilutive securities									183	5	192
Weighted-average shares outstanding — Diluted	64,917	64,776	64,857	64,054	63,888	63,708	63,530	62,643	64,600	63,440	62,010
Net income per common share — Diluted	$ 0.06	$ 0.07	$ 0.20	$ 0.04	$ (0.17)	$ 0.02	$ 0.13	$ 0.06	$ 0.38	$ 0.04	$ 0.29