Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Income Statement Data Abstract
Net interest income	$ 676,278	$ 680,967	$ 645,543
Noninterest income	328,409	290,319	313,099
Total income	1,004,687	971,286	958,642
Provision for credit losses	37,500	16,000	10,100
Noninterest expense	697,399	679,241	680,649
Income before income taxes	269,788	276,045	267,893
Income tax expense	81,487	85,536	79,201
Net income	$ 188,301	$ 190,509	$ 188,692
Return on average allocated capital (ROCET1)	9.90%	9.90%	9.80%
Segment Balance Sheet Data
Average earning assets	$ 24,571,087	$ 22,760,128	$ 20,980,128
Average loans	18,252,264	16,838,994	15,663,145
Average deposits	19,903,087	17,647,084	17,438,195
Average allocated capital (CET1)	1,833,597	1,870,609	1,878,371
Operating Segments [Member] | Commercial Banking Segment [Member]
Segment Income Statement Data Abstract
Net interest income	310,072	296,717	321,346
Noninterest income	46,742	49,213	48,417
Total income	356,814	345,930	369,763
Provision for credit losses	41,913	46,857	55,297
Noninterest expense	141,912	148,476	140,744
Income before income taxes	172,989	150,597	173,722
Income tax expense	59,200	50,039	60,802
Net income	$ 113,789	$ 100,558	$ 112,920
Return on average allocated capital (ROCET1)	11.60%	11.10%	12.50%
Segment Balance Sheet Data
Average earning assets	$ 9,383,971	$ 8,927,401	$ 8,443,203
Average loans	9,374,191	8,915,498	8,433,389
Average deposits	5,856,530	5,148,195	5,479,567
Average allocated capital (CET1)	977,406	903,500	900,306
Operating Segments [Member] | Community, Consumer, and Business [Member]
Segment Income Statement Data Abstract
Net interest income	349,134	310,444	317,898
Noninterest income	265,638	221,379	247,667
Total income	614,772	531,823	565,565
Provision for credit losses	25,614	23,934	20,122
Noninterest expense	492,419	463,184	477,318
Income before income taxes	96,739	44,705	68,125
Income tax expense	33,859	15,647	23,843
Net income	$ 62,880	$ 29,058	$ 44,282
Return on average allocated capital (ROCET1)	9.80%	5.10%	7.80%
Segment Balance Sheet Data
Average earning assets	$ 8,810,015	$ 7,840,352	$ 7,225,943
Average loans	8,809,673	7,840,352	7,225,943
Average deposits	10,898,602	10,061,495	9,675,302
Average allocated capital (CET1)	640,181	564,303	570,634
Operating Segments [Member] | Risk Management and Shared Services [Member]
Segment Income Statement Data Abstract
Net interest income	17,072	73,806	6,299
Noninterest income	16,029	19,727	17,015
Total income	33,101	93,533	23,314
Provision for credit losses	(30,027)	(54,791)	(65,319)
Noninterest expense	63,068	67,581	62,587
Income before income taxes	60	80,743	26,046
Income tax expense	(11,572)	19,850	(5,444)
Net income	$ 11,632	$ 60,893	$ 31,490
Return on average allocated capital (ROCET1)	2.10%	13.90%	6.50%
Segment Balance Sheet Data
Average earning assets	$ 6,377,101	$ 5,992,375	$ 5,310,982
Average loans	68,400	83,144	3,813
Average deposits	3,147,955	2,437,394	2,283,326
Average allocated capital (CET1)	$ 216,010	$ 402,806	$ 407,431