Earnings per Common Share - Diluted 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
Diluted weighted-average Class A shares issued and outstanding (in shares)									53,138	54,481	53,198
Diluted earnings per common share (in USD per share)	$ 0.03	$ (0.01)	$ 0.64	$ 1.17	$ 0.26	$ 0.08	$ 0.55	$ 1.29	$ 1.88	$ 2.18	$ 1.61
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive potential common shares (in shares)									114	327	809
Restricted Stock Units (RSUs)
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive potential common shares (in shares)									361	1,135	1,445
Performance Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive potential common shares (in shares)									440	796	462
Employee stock purchase plan
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive potential common shares (in shares)									28	1	0
Retained Earnings
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income									$ 99,897	$ 118,703	$ 85,887