Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	$ 72,719	$ 65,251	$ 218,270	$ 195,149
Noninterest Income (out-of-scope of Topic 606)	15,581	20,644	53,252	52,987
Total noninterest income	88,300	85,895	271,522	248,136
Insurance commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	21,636	19,815	68,279	62,288
Deposit Account
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	16,904	16,268	49,714	48,654
Card-Based and No Loan Fees [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	10,155	9,124	30,587	26,700
Fiduciary and Trust
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	14,140	12,785	40,946	37,066
Brokerage commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	7,084	4,392	21,253	13,071
Other revenue
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	2,800	2,868	7,491	7,370
Corporate and Commercial Specialty
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	4,110	4,617	12,625	13,801
Noninterest Income (out-of-scope of Topic 606)	8,170	7,661	26,531	22,967
Corporate and Commercial Specialty | Insurance commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	0	0	0	0
Corporate and Commercial Specialty | Deposit Account
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	3,669	3,824	11,680	12,334
Corporate and Commercial Specialty | Card-Based and No Loan Fees [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	349	284	1,023	876
Corporate and Commercial Specialty | Fiduciary and Trust
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	0	0	0	0
Corporate and Commercial Specialty | Brokerage commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	0	0	0	0
Corporate and Commercial Specialty | Other revenue
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	92	509	(78)	591
Community, Consumer, and Business
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	68,503	60,566	205,036	181,115
Noninterest Income (out-of-scope of Topic 606)	5,335	7,301	19,073	17,431
Community, Consumer, and Business | Insurance commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	21,632	19,813	68,244	62,286
Community, Consumer, and Business | Deposit Account
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	13,210	12,432	37,984	36,259
Community, Consumer, and Business | Card-Based and No Loan Fees [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	9,821	8,834	29,512	25,807
Community, Consumer, and Business | Fiduciary and Trust
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	14,140	12,784	40,946	37,066
Community, Consumer, and Business | Brokerage commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	7,114	4,392	21,001	13,071
Community, Consumer, and Business | Other revenue
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	2,586	2,311	7,349	6,626
Risk Management and Shared Services
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	106	68	611	233
Noninterest Income (out-of-scope of Topic 606)	2,077	5,682	7,646	12,589
Risk Management and Shared Services | Insurance commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	4	2	36	2
Risk Management and Shared Services | Deposit Account
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	25	12	50	61
Risk Management and Shared Services | Card-Based and No Loan Fees [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	(15)	6	52	17
Risk Management and Shared Services | Fiduciary and Trust
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	0	0	0	0
Risk Management and Shared Services | Brokerage commissions and fees
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	(30)	0	252	0
Risk Management and Shared Services | Other revenue
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Noninterest Income In Scope of Topic 606	$ 122	$ 48	$ 221	$ 153