Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Net income available to common stockholders	$ 254,852	$ 237,828	$ 215,713
Average common shares outstanding (in shares)	109,860	98,351	92,268
Average potential dilutive common shares (in shares)	313	446	562
Average diluted common shares (in shares)	110,173	98,797	92,830
Basic earnings per share (in dollars per share)	$ 2.32	$ 2.42	$ 2.34
Diluted earnings per share (in dollars per share)	$ 2.31	$ 2.41	$ 2.32