Net Income Per Share - Reconciliation of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 73,778	$ 67,057	$ 196,650	$ 157,362
Basic weighted-average shares outstanding	43,276	43,474	43,287	43,683
Dilutive effect of potential common stock equivalents — restricted stock units	209	209	213	190
Diluted weighted-average shares outstanding	43,485	43,683	43,500	43,873
Net income per common share:
Basic	$ 1.70	$ 1.54	$ 4.54	$ 3.60
Diluted	$ 1.70	$ 1.54	$ 4.52	$ 3.59