Earnings Per Share - Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 84,396	$ 36,760	$ 54,593	$ 40,550	$ 121,156	$ 95,143
Less: distributed earnings allocated to participating securities	(121)		(110)		(256)	(221)
Less: undistributed earnings allocated to participating securities	(363)		(213)		(465)	(352)
Net income attributable to common stockholders (numerator for basic earnings per share)	83,912		54,270		120,435	94,570
Add back: undistributed earnings allocated to participating securities	363		213		465	352
Less: undistributed earnings reallocated to participating securities	(357)		(209)		(455)	(345)
Numerator for diluted earnings per share under two class method	$ 83,918		$ 54,274		$ 120,445	$ 94,577
Weighted-average common shares outstanding	63,015,827		61,336,404		62,755,310	61,138,982
Denominator for diluted earnings per share under two class method	64,080,940		63,323,267		64,538,835	63,023,149
Basic Earnings Per Common Share (in dollars per share)	$ 1.33		$ 0.88		$ 1.92	$ 1.55
Diluted Earnings Per Common Share (in dollars per share)	$ 1.31		$ 0.86		$ 1.87	$ 1.50
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	1,065,113		1,435,739		1,494,841	1,333,043
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	0		551,124		288,684	551,124