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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 67,057	$ 43,686	$ 157,362	$ 105,925
Basic weighted-average shares outstanding	43,474	44,477	43,683	44,673
Dilutive effect of potential common stock equivalents — restricted stock units	209	337	190	322
Diluted weighted-average shares outstanding	43,683	44,814	43,873	44,995
Earnings per common share:
Basic	$ 1.54	$ 0.98	$ 3.60	$ 2.37
Diluted	$ 1.54	$ 0.97	$ 3.59	$ 2.35