Loans and Leases - Summary of Consumer Loans by Payment Status (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Credit Quality [Line Items]
Total Loans	$ 20,177,650	$ 14,896,943
Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	105,378	85,907
Direct Installment [Member]
Credit Quality [Line Items]
Total Loans	1,965,118	1,844,399
Residential Mortgages [Member]
Credit Quality [Line Items]
Total Loans	2,342,167	1,844,574
Indirect Installment [Member]
Credit Quality [Line Items]
Total Loans	1,259,947	1,196,313
Originated Loans and Leases [Member]
Credit Quality [Line Items]
Total Loans	13,034,528	12,547,987
Originated Loans and Leases [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	5,671,288	5,507,770
Originated Loans and Leases [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	5,636,346	5,474,286
Originated Loans and Leases [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	34,942	33,484
Originated Loans and Leases [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Total Loans	1,758,895	1,765,257
Originated Loans and Leases [Member] | Direct Installment [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	1,758,895	1,765,257
Originated Loans and Leases [Member] | Direct Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,742,702	1,750,305
Originated Loans and Leases [Member] | Direct Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	16,193	14,952
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Total Loans	1,551,928	1,446,776
Originated Loans and Leases [Member] | Residential Mortgages [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	1,551,928	1,446,776
Originated Loans and Leases [Member] | Residential Mortgages [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,537,779	1,433,409
Originated Loans and Leases [Member] | Residential Mortgages [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	14,149	13,367
Originated Loans and Leases [Member] | Indirect Installment [Member]
Credit Quality [Line Items]
Total Loans	1,259,770	1,196,110
Originated Loans and Leases [Member] | Indirect Installment [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	1,259,770	1,196,110
Originated Loans and Leases [Member] | Indirect Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,258,084	1,193,930
Originated Loans and Leases [Member] | Indirect Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	1,686	2,180
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	1,100,695	1,099,627
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,097,781	1,096,642
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	2,914	2,985
Acquired Loans [Member]
Credit Quality [Line Items]
Total Loans	7,143,122	2,348,956
Acquired Loans [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	1,701,940	678,716
Acquired Loans [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	1,698,943	678,204
Acquired Loans [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	2,997	512
Acquired Loans [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Total Loans	206,223	79,142
Acquired Loans [Member] | Direct Installment [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	206,223	79,142
Acquired Loans [Member] | Direct Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	206,138	79,142
Acquired Loans [Member] | Direct Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	85
Acquired Loans [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Total Loans	790,239	397,798
Acquired Loans [Member] | Residential Mortgages [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	790,239	397,798
Acquired Loans [Member] | Residential Mortgages [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	788,656	397,798
Acquired Loans [Member] | Residential Mortgages [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	1,583
Acquired Loans [Member] | Indirect Installment [Member]
Credit Quality [Line Items]
Total Loans	177	203
Acquired Loans [Member] | Indirect Installment [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	177	203
Acquired Loans [Member] | Indirect Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	177	203
Acquired Loans [Member] | Consumer Lines of Credit [Member] | Consumer Loan [Member]
Credit Quality [Line Items]
Total Loans	705,301	201,573
Acquired Loans [Member] | Consumer Lines of Credit [Member] | Performing [Member]
Credit Quality [Line Items]
Performing Loans	703,972	201,061
Acquired Loans [Member] | Consumer Lines of Credit [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Non-Performing Loans	$ 1,329	$ 512