Net income Per Share - Reconciliation of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 72,483	$ 53,479	$ 122,872	$ 90,305
Basic weighted-average shares outstanding	43,434	43,471	43,406	43,787
Dilutive effect of potential common stock equivalents — restricted stock units	207	192	214	193
Diluted weighted-average shares outstanding	43,641	43,663	43,620	43,980
Net income per common share:
Basic	$ 1.67	$ 1.23	$ 2.83	$ 2.06
Diluted	$ 1.66	$ 1.22	$ 2.82	$ 2.05