Net Income Per Common Share - Basic and Diluted Net Income Per Common 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
Basic
Net income applicable to common stock	$ 29,992	$ 20,130	$ 2,008	$ 37,446	$ 46,625	$ 45,110	$ 52,130	$ 129,181
Average common shares outstanding (shares)	56,185,884			58,003,215			56,294,984	58,347,840
Net income per common share - basic (usd per share)	$ 0.53			$ 0.65			$ 0.93	$ 2.21
Diluted
Net income applicable to common stock	$ 29,992	$ 20,130	$ 2,008	$ 37,446	$ 46,625	$ 45,110	$ 52,130	$ 129,181
Average common shares outstanding (shares)	56,185,884			58,003,215			56,294,984	58,347,840
Effect of dilutive stock-based compensation (shares)	200,269			189,204			173,593	160,742
Average common shares outstanding - diluted (shares)	56,386,153			58,192,419			56,468,577	58,508,582
Net income per common share - diluted (usd per share)	$ 0.53			$ 0.64			$ 0.92	$ 2.21