Selected Quarterly Financial Data Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Income (Expense), Net [Abstract]
Interest Income	$ 284,597	$ 260,966	$ 259,544	$ 247,409	$ 261,773	$ 247,855	$ 247,054	$ 259,230	$ 1,052,516	$ 1,015,912	$ 883,938
Interest expense	(21,641)	(19,276)	(17,071)	(14,957)	(13,468)	(13,220)	(13,297)	(14,636)	(72,945)	(54,621)	(60,592)
Net interest income	262,956	241,690	242,473	232,452	248,305	234,635	233,757	244,594	979,571	961,291	823,346
Provision for credit losses	6,406	15,119	11,499	24,728	23,215	8,471	13,903	(20,140)	57,752	65,729	45,481
FDIC loss sharing expense, net					0	0	(6,502)	(2,415)	0	(8,917)	(18,246)
Noninterest Income [Abstract]
(Loss) gain on sale of securities	(3,329)	1,236	1,651	(99)	515	382	478	8,110	(541)	9,485	3,744
Noninterest Income, Other	30,124	30,146	33,631	35,213	28,380	26,538	28,145	28,844
Total noninterest income	26,795	31,382	35,282	35,114	28,895	26,920	22,121	34,539	128,573	112,475	84,310
Foreclosed Assets (Income) Expense, Net	475	(2,191)	157	(143)	(2,693)	248	3	561
Noninterest Expense [Abstract]
Amortization	(16,085)	(1,450)	(1,700)	(500)	0	0	0	(200)	(14,240)	(16,517)	(9,410)
Acquisition, integration and reorganization costs	(127,258)	(114,901)	(116,164)	(115,901)	(115,929)	(110,958)	(110,084)	(111,049)	(19,735)	(200)	(21,247)
Total noninterest expense	(142,868)	(118,542)	(117,707)	(116,544)	(118,622)	(110,710)	(110,081)	(110,688)	(495,661)	(450,101)	(382,039)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent [Abstract]
Earnings from continuing operations before taxes	140,477	139,411	148,549	126,294	135,363	142,374	131,894	148,305	554,731	557,936	480,136
Income Tax Expense (Benefit)	(56,440)	(37,945)	54,902	47,626	(49,716)	(48,479)	(49,726)	(57,849)	(196,913)	(205,770)	(180,517)
Net earnings	$ 84,037	$ 101,466	$ 93,647	$ 78,668					$ 357,818	$ 352,166	$ 299,619
Net earnings from continuing operations					$ 85,647	$ 93,895	$ 82,168	$ 90,456
Earnings Per Share, Basic [Abstract]
Basic and diluted earnings per share (usd per share)	$ 0.66	$ 0.84	$ 0.77	$ 0.65	$ 0.71	$ 0.77	$ 0.68	$ 0.74