Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	$ 274,264	$ 266,302
Charge offs	(74,830)	(52,280)
Recoveries	19,106	22,242
Net charge offs	(55,724)	(30,038)
Provision for loan losses	51,000	38,000
Balance at end of period	269,540	274,264
Allowance for loan losses:
Individually evaluated for impairment	9,625	7,963
Collectively evaluated for impairment	259,915	266,301
Balance at end of period	269,540	274,264
Loans:
Individually evaluated for impairment	226,615	111,487
Collectively evaluated for impairment	19,617,390	18,602,856
Total loans	19,844,005	18,714,343
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	129,959	117,635
Charge offs	(63,368)	(27,687)
Recoveries	13,461	9,821
Net charge offs	(49,907)	(17,866)
Provision for loan losses	57,051	30,190
Balance at end of period	137,103	129,959
Allowance for loan losses:
Individually evaluated for impairment	8,570	7,522
Collectively evaluated for impairment	128,533	122,437
Balance at end of period	137,103	129,959
Loans:
Individually evaluated for impairment	203,834	91,569
Collectively evaluated for impairment	6,517,723	6,099,114
Total loans	6,721,557	6,190,683
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	18,680	16,510
Charge offs	(265)	(2,645)
Recoveries	48	921
Net charge offs	(217)	(1,724)
Provision for loan losses	(4,106)	3,894
Balance at end of period	14,357	18,680
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	14,357	18,680
Balance at end of period	14,357	18,680
Loans:
Individually evaluated for impairment	5,719	6,221
Collectively evaluated for impairment	886,959	911,991
Total loans	892,678	918,212
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	43,018	46,333
Charge offs	(1,495)	(4,645)
Recoveries	1,610	4,157
Net charge offs	115	(488)
Provision for loan losses	(2,366)	(2,827)
Balance at end of period	40,767	43,018
Allowance for loan losses:
Individually evaluated for impairment	79	229
Collectively evaluated for impairment	40,688	42,789
Balance at end of period	40,767	43,018
Loans:
Individually evaluated for impairment	7,023	5,460
Collectively evaluated for impairment	3,523,347	3,228,806
Total loans	3,530,370	3,234,266
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	25,266	20,999
Charge offs	(380)	(750)
Recoveries	111	2,268
Net charge offs	(269)	1,518
Provision for loan losses	(1,873)	2,749
Balance at end of period	23,124	25,266
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	23,124	25,266
Balance at end of period	23,124	25,266
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,314,431	1,162,145
Total loans	1,314,431	1,162,145
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	28,261	31,926
Charge offs	(3,035)	(5,636)
Recoveries	506	1,077
Net charge offs	(2,529)	(4,559)
Provision for loan losses	1,121	894
Balance at end of period	26,853	28,261
Allowance for loan losses:
Individually evaluated for impairment	976	166
Collectively evaluated for impairment	25,877	28,095
Balance at end of period	26,853	28,261
Loans:
Individually evaluated for impairment	9,389	6,956
Collectively evaluated for impairment	6,024,777	5,776,311
Total loans	6,034,166	5,783,267
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	23,555	26,464
Charge offs	(3,434)	(7,048)
Recoveries	2,730	3,233
Net charge offs	(704)	(3,815)
Provision for loan losses	(897)	906
Balance at end of period	21,954	23,555
Allowance for loan losses:
Individually evaluated for impairment	0	46
Collectively evaluated for impairment	21,954	23,509
Balance at end of period	21,954	23,555
Loans:
Individually evaluated for impairment	650	1,281
Collectively evaluated for impairment	950,944	1,004,521
Total loans	951,594	1,005,802
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	5,525	6,435
Charge offs	(2,853)	(3,869)
Recoveries	640	765
Net charge offs	(2,213)	(3,104)
Provision for loan losses	2,070	2,194
Balance at end of period	5,382	5,525
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	5,382	5,525
Balance at end of period	5,382	5,525
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	399,209	419,968
Total loans	$ 399,209	$ 419,968