Earnings per Common Share - Basic Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 1,693	$ (531)	$ 34,692	$ 64,043	$ 14,272	$ 4,573	$ 29,827	$ 70,031	$ 99,897	$ 118,703	$ 85,887
Weighted-average Class A shares issued and outstanding (in shares)									52,195	52,222	50,482
Basic earnings per common share (in USD per share)	$ 0.03	$ (0.01)	$ 0.66	$ 1.21	$ 0.27	$ 0.09	$ 0.57	$ 1.36	$ 1.91	$ 2.27	$ 1.70
Retained Earnings
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income									$ 99,897	$ 118,703	$ 85,887