Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 85,964	$ 99,121	$ 81,466	$ 89,146	$ 79,657	$ 91,948	$ 89,580	$ 81,981	$ 355,697	$ 343,166	$ 257,682
Less: Preferred stock dividends	2,050	2,050	2,050	2,050	2,050	2,050	2,050	2,050	8,200	8,200	9,778
Net income applicable to common shares	$ 83,914	$ 97,071	$ 79,416	$ 87,096	$ 77,607	$ 89,898	$ 87,530	$ 79,931	347,497	334,966	247,904
Add: Dividends on convertible preferred stock, if dilutive									0	0	1,578
Net income applicable to common shares—Diluted									$ 347,497	$ 334,966	$ 249,482
Weighted average common shares outstanding (in shares)									56,857	56,300	54,703
Common stock equivalents (in shares)									762	908	998
Convertible preferred stock, if dilutive (in shares)									0	0	985
Total dilutive potential common shares (in shares)									762	908	1,983
Weighted average common shares and effect of dilutive potential common shares (in shares)									57,619	57,208	56,686
Net income per common share:
Basic (usd per share)	$ 1.46	$ 1.71	$ 1.40	$ 1.54	$ 1.38	$ 1.59	$ 1.55	$ 1.42	$ 6.11	$ 5.95	$ 4.53
Diluted (usd per share)	$ 1.44	$ 1.69	$ 1.38	$ 1.52	$ 1.35	$ 1.57	$ 1.53	$ 1.40	$ 6.03	$ 5.86	$ 4.40