Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 101,204	$ 107,315	$ 21,659	$ 62,812	$ 85,964	$ 99,121	$ 81,466	$ 89,146	$ 292,990	$ 355,697	$ 343,166
Preferred stock dividends	$ 6,991	$ 10,286	$ 2,050	$ 2,050	$ 2,050	$ 2,050	$ 2,050	$ 2,050	21,377	8,200	8,200
Net income applicable to common shares									$ 271,613	$ 347,497	$ 334,966
Weighted average common shares outstanding (in shares)									57,523	56,857	56,300
Effect of dilutive potential common shares:
Common stock equivalents (in shares)									496	762	908
Average common shares and dilutive common shares (in shares)									58,019	57,619	57,208
Net income per common share:
Basic (usd per share)	$ 1.64	$ 1.68	$ 0.34	$ 1.05	$ 1.46	$ 1.71	$ 1.40	$ 1.54	$ 4.72	$ 6.11	$ 5.95
Diluted (usd per share)	$ 1.63	$ 1.67	$ 0.34	$ 1.04	$ 1.44	$ 1.69	$ 1.38	$ 1.52	$ 4.68	$ 6.03	$ 5.86