Earnings per Common Share - Basic Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 3,294	$ 34,692	$ 50,139	$ 98,735
Net income allocated to Class A common stockholders	$ 3,242	$ 34,692	$ 49,311	$ 98,735
Basic weighted-average common shares issued and outstanding (in shares)	52,275	52,588	52,084	52,818
Basic earnings per common share (in usd per share)	$ 0.06	$ 0.66	$ 0.95	$ 1.87
Earnings Per Share, Diluted [Abstract]
Net income allocated to Class A common stockholders	$ 3,242	$ 34,692	$ 49,311	$ 98,735
Re-allocated earnings	1	0	13	0
Diluted net income allocated to Class A common stockholders	$ 3,243	$ 34,692	$ 49,324	$ 98,735
Basic weighted-average common shares issued and outstanding (in shares)	52,275	52,588	52,084	52,818
Diluted weighted-average Class A shares issued and outstanding (in shares)	53,164	53,811	52,913	54,154
Diluted earnings per common share (in usd per share)	$ 0.06	$ 0.64	$ 0.93	$ 1.82
Other Classes of Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income allocated to Class A common stockholders	$ (52)	$ 0	$ (828)	$ 0
Earnings Per Share, Diluted [Abstract]
Net income allocated to Class A common stockholders	(52)	0	(828)	0
Common Class A
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income allocated to Class A common stockholders	3,242	34,692	49,311	98,735
Earnings Per Share, Diluted [Abstract]
Net income allocated to Class A common stockholders	$ 3,242	$ 34,692	$ 49,311	$ 98,735
Stock options
Earnings Per Share, Diluted [Abstract]
Dilutive potential common shares (in shares)	58	131	57	150
Restricted stock units
Earnings Per Share, Diluted [Abstract]
Dilutive potential common shares (in shares)	567	456	469	586
Performance-based restricted stock units
Earnings Per Share, Diluted [Abstract]
Dilutive potential common shares (in shares)	258	630	299	592
Employee stock purchase plan
Earnings Per Share, Diluted [Abstract]
Dilutive potential common shares (in shares)	6	6	4	8