Selected Quarterly Financial Data Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ 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
Interest Income (Expense), Net [Abstract]
Total interest income	$ 272,176	$ 265,908	$ 274,075	$ 291,332	$ 293,593	$ 307,208	$ 314,533	$ 304,559	$ 1,103,491	$ 1,219,893	$ 1,161,670
Interest expense	(12,968)	(14,584)	(19,796)	(41,585)	(46,974)	(54,972)	(53,635)	(49,683)	(88,933)	(205,264)	(120,756)
Net interest income	259,208	251,324	254,279	249,747	246,619	252,236	260,898	254,876	1,014,558	1,014,629	1,040,914
Provision for credit losses	(10,000)	(97,000)	(120,000)	(112,000)	(3,000)	(7,000)	(8,000)	(4,000)	(339,000)	(22,000)	(45,000)
Interest Income (Expense), after Provision for Loan Loss	249,208	154,324	134,279	137,747	243,619	245,236	252,898	250,876	675,558	992,629	995,914
Noninterest Income [Abstract]
Gain on sale of securities	4	5,270	7,715	182	184	908	22,192	2,161	13,171	25,445	8,176
Noninterest Income, Other	39,846	32,982	31,143	28,918	26,992	32,521	28,701	28,903
Total noninterest income	39,850	38,252	38,858	29,100	27,176	33,429	50,893	31,064	146,060	142,562	148,635
Foreclosed Assets (Income) Expense, Net	272	(335)	146	(66)	3,446	(8)	146	(29)
Noninterest Expense [Abstract]
Acquisition, integration and reorganization costs	(1,060)	0	0	0	269	0	0	(618)
Other expense	134,894	133,067	127,111	117,904	127,443	126,801	125,573	125,640	40,002	30,913	39,741
Total noninterest expense	(135,682)	(133,402)	(126,965)	(1,587,970)	(123,728)	(126,809)	(125,427)	(126,287)	(1,984,019)	(502,251)	(511,232)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent [Abstract]
Earnings from continuing operations before taxes	153,376	59,174	46,172	(1,421,123)	147,067	151,856	178,364	155,653	(1,162,401)	632,940	633,317
Income Tax Expense (Benefit)	(36,546)	(13,671)	(12,968)	(11,988)	(29,186)	(41,830)	(50,239)	(43,049)	(75,173)	(164,304)	(167,978)
Net earnings (loss)	$ 116,830	$ 45,503	$ 33,204	$ (1,433,111)	$ 117,881	$ 110,026	$ 128,125	$ 112,604	$ (1,237,574)	$ 468,636	$ 465,339
Earnings Per Share, Diluted	$ 0.99	$ 0.38	$ 0.28	$ (12.23)	$ 0.98	$ 0.92	$ 1.07	$ 0.92	$ (10.61)	$ 3.90	$ 3.72
Earnings Per Share, Basic (usd per share)	0.99	0.38	0.28	(12.23)	0.98		1.07	0.92	(10.61)	3.90	3.72
Earnings Per Share, Basic [Abstract]
Dividends declared per share (usd per share)	$ 0.25	$ 0.25	$ 0.25	$ 0.60	$ 0.60	$ 0.60	$ 0.60	$ 0.60	$ 2.30	$ 2.40	$ 1.35
Goodwill, Impairment Loss	$ 0	$ 0	$ 0	$ (1,470,000)					$ (1,470,000)	$ 0	$ 0