Earnings Per Common Share - Calculation of basic and diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 15,539	$ 14,510	$ 13,267	$ 14,607	$ 2,252	$ 11,311	$ 2,030	$ 10,281	$ 57,923	$ 25,874	$ 29,353
Less: Net income allocated to participating securities									(364)	(354)	(260)
Numerator for basic and diluted earnings available to common stockholders									$ 57,559	$ 25,520	$ 29,093
Denominator:
Weighted-average basic common shares outstanding (shares)	84,059	81,490	76,374	75,504	75,476	75,471	72,564	66,951	79,386	72,647	56,030
Weighted-average diluted common shares outstanding (shares)	84,084	81,490	76,374	75,504	75,476	75,471	72,564	66,951	79,392	72,647	56,030
Earnings per common share, basic (usd per share)	$ 0.18	$ 0.18	$ 0.17	$ 0.19	$ 0.03	$ 0.15	$ 0.03	$ 0.15	$ 0.73	$ 0.35	$ 0.52
Earnings per common share, diluted (usd per share)	$ 0.18	$ 0.18	$ 0.17	$ 0.19	$ 0.03	$ 0.15	$ 0.03	$ 0.15	$ 0.72	$ 0.35	$ 0.52