Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2017	Dec. 31, 2016
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	$ 278,335	$ 274,264
Charge offs	(41,957)	(86,439)
Recoveries	13,173	21,510
Net Charge offs	(28,784)	(64,929)
Provision for loan losses	27,000	69,000
Balance at end of period	276,551	278,335
Allowance for loan losses:
Individually evaluated			$ 25,671	$ 35,054
Collectively evaluated			250,880	243,281
Total allowance for loan losses	276,551	278,335	276,551	278,335
Loans:
Individually evaluated			252,542	316,735
Collectively evaluated			20,678,918	19,737,981
Total loans			20,931,460	20,054,716
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	140,126	129,959
Charge offs	(33,928)	(71,016)
Recoveries	9,072	14,543
Net Charge offs	(24,856)	(56,473)
Provision for loan losses	23,587	66,640
Balance at end of period	138,857	140,126
Allowance for loan losses:
Individually evaluated			11,540	21,047
Collectively evaluated			127,317	119,079
Total allowance for loan losses	138,857	129,959	138,857	140,126
Loans:
Individually evaluated			154,028	213,271
Collectively evaluated			6,380,632	6,275,743
Total loans			6,534,660	6,489,014
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	14,034	18,680
Charge offs	(83)	(512)
Recoveries	158	74
Net Charge offs	75	(438)
Provision for loan losses	(4,352)	(4,208)
Balance at end of period	9,757	14,034
Allowance for loan losses:
Individually evaluated			1,549	23
Collectively evaluated			8,208	14,011
Total allowance for loan losses	9,757	18,680	9,757	14,034
Loans:
Individually evaluated			19,126	13,983
Collectively evaluated			807,938	883,741
Total loans			827,064	897,724
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	45,285	43,018
Charge offs	(803)	(1,504)
Recoveries	218	1,624
Net Charge offs	(585)	120
Provision for loan losses	1,798	2,147
Balance at end of period	46,498	45,285
Allowance for loan losses:
Individually evaluated			1,812	3,410
Collectively evaluated			44,686	41,875
Total allowance for loan losses	45,285	45,285	46,498	45,285
Loans:
Individually evaluated			17,563	32,908
Collectively evaluated			3,327,973	3,541,824
Total loans			3,345,536	3,574,732
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	26,932	25,266
Charge offs	(225)	(558)
Recoveries	60	203
Net Charge offs	(165)	(355)
Provision for loan losses	(1,340)	2,021
Balance at end of period	25,427	26,932
Allowance for loan losses:
Individually evaluated			75	84
Collectively evaluated			25,352	26,848
Total allowance for loan losses	25,427	25,266	25,427	26,932
Loans:
Individually evaluated			689	509
Collectively evaluated			1,551,446	1,431,988
Total loans			1,552,135	1,432,497
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	27,046	28,261
Charge offs	(1,472)	(4,332)
Recoveries	754	755
Net Charge offs	(718)	(3,577)
Provision for loan losses	4,632	2,362
Balance at end of period	30,960	27,046
Allowance for loan losses:
Individually evaluated			6,893	6,438
Collectively evaluated			24,067	20,608
Total allowance for loan losses	27,046	27,046	30,960	27,046
Loans:
Individually evaluated			49,153	43,876
Collectively evaluated			7,359,318	6,288,451
Total loans			7,408,471	6,332,327
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	20,364	23,555
Charge offs	(2,208)	(4,686)
Recoveries	2,348	3,491
Net Charge offs	140	(1,195)
Provision for loan losses	(479)	(1,996)
Balance at end of period	20,025	20,364
Allowance for loan losses:
Individually evaluated			3,684	3,943
Collectively evaluated			16,341	16,421
Total allowance for loan losses	20,025	23,555	20,025	20,364
Loans:
Individually evaluated			10,891	11,176
Collectively evaluated			879,239	923,267
Total loans			890,130	934,443
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	4,548	5,525
Charge offs	(3,238)	(3,831)
Recoveries	563	820
Net Charge offs	(2,675)	(3,011)
Provision for loan losses	3,154	2,034
Balance at end of period	5,027	4,548
Allowance for loan losses:
Individually evaluated			118	109
Collectively evaluated			4,909	4,439
Total allowance for loan losses	$ 5,027	$ 5,525	5,027	4,548
Loans:
Individually evaluated			1,092	1,012
Collectively evaluated			372,372	392,967
Total loans			$ 373,464	$ 393,979