Earnings Per Share - Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 98,938	$ 84,396	$ 36,760	$ 50,580	$ 54,593	$ 40,550	$ 220,094	$ 145,723
Less: distributed earnings allocated to participating securities	(148)			(122)			(404)	(343)
Less: undistributed earnings allocated to participating securities	(502)			(202)			(952)	(554)
Net income attributable to common stockholders (numerator for basic earnings per share)	98,288			50,256			218,738	144,826
Add back: undistributed earnings allocated to participating securities	502			202			952	554
Less: undistributed earnings reallocated to participating securities	(488)			(195)			(929)	(540)
Numerator for diluted earnings per share under two class method	$ 98,302			$ 50,263			$ 218,761	$ 144,840
Weighted-average common shares outstanding	63,868,486			61,978,195			63,129,077	61,422,925
Denominator for diluted earnings per share under two class method	65,824,910			63,968,215			64,969,855	63,360,535
Basic Earnings Per Common Share (in dollars per share)	$ 1.54			$ 0.81			$ 3.46	$ 2.36
Diluted Earnings Per Common Share (in dollars per share)	$ 1.49			$ 0.79			$ 3.37	$ 2.29
Stock option grants expense
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average common shares outstanding, dilutive effect of stock options and performance share units	1,810,624			1,990,020			1,599,722	1,570,194
Performance Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average common shares outstanding, dilutive effect of stock options and performance share units	145,800			0			241,056	367,416