Loans and Leases - Age Analysis of Past Due Loans, by Class (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	$ 20,998,766	$ 14,896,943
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	8,741,864	5,435,162
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	4,170,667	3,042,781
Commercial leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	266,720	196,636
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	17,063	35,878
Total commercial loans and leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	13,196,314	8,710,457
Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	1,905,535	1,844,399
Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	2,702,691	1,844,574
Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	1,448,433	1,196,313
Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	1,745,793	1,301,200
Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	7,802,452	6,186,486
Originated Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	63,644	62,083
Total Past Due	134,911	131,046
Current	15,210,579	12,416,941
Total Loans and Leases	15,345,490	12,547,987
Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	24,773	20,114
Total Past Due	33,047	28,567
Current	5,141,736	4,067,250
Total Loans and Leases	5,174,783	4,095,817
Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	17,077	24,141
Total Past Due	26,028	40,163
Current	3,469,219	2,671,723
Total Loans and Leases	3,495,247	2,711,886
Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	1,574	3,429
Total Past Due	2,997	4,403
Current	263,723	192,233
Total Loans and Leases	266,720	196,636
Originated Loans and Leases | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	1,000	1,000
Total Past Due	1,236	1,481
Current	15,827	34,397
Total Loans and Leases	17,063	35,878
Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	44,424	48,684
Total Past Due	63,308	74,614
Current	8,890,505	6,965,603
Total Loans and Leases	8,953,813	7,040,217
Originated Loans and Leases | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	8,896	6,484
Total Past Due	26,554	21,443
Current	1,729,159	1,743,814
Total Loans and Leases	1,755,713	1,765,257
Originated Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	5,771	3,316
Total Past Due	22,699	16,924
Current	2,013,527	1,429,852
Total Loans and Leases	2,036,226	1,446,776
Originated Loans and Leases | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	2,240	1,983
Total Past Due	13,164	11,808
Current	1,435,104	1,184,302
Total Loans and Leases	1,448,268	1,196,110
Originated Loans and Leases | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	2,313	1,616
Total Past Due	9,186	6,257
Current	1,142,284	1,093,370
Total Loans and Leases	1,151,470	1,099,627
Originated Loans and Leases | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	19,220	13,399
Total Past Due	71,603	56,432
Current	6,320,074	5,451,338
Total Loans and Leases	6,391,677	5,507,770
Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	10,991	3,396
Total Past Due	167,867	68,130
Current	5,768,610	2,430,340
(Discount)/ Premium	(283,201)	(149,514)
Total Loans and Leases	5,653,276	2,348,956
Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	3,975	949
Total Past Due	101,995	34,340
Current	3,657,152	1,384,752
(Discount)/ Premium	(192,066)	(79,747)
Total Loans and Leases	3,567,081	1,339,345
Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	5,663	2,111
Total Past Due	15,302	6,842
Current	698,265	353,494
(Discount)/ Premium	(38,147)	(29,441)
Total Loans and Leases	675,420	330,895
Acquired Loans | Total commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	9,638	3,060
Total Past Due	117,297	41,182
Current	4,355,417	1,738,246
(Discount)/ Premium	(230,213)	(109,188)
Total Loans and Leases	4,242,501	1,670,240
Acquired Loans | Commercial leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	0	0
Acquired Loans | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	0	0
Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans and Leases	4,242,501	1,670,240
Acquired Loans | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Total Past Due	7,280	3,661
Current	141,386	73,479
(Discount)/ Premium	1,156	2,002
Total Loans and Leases	149,822	79,142
Acquired Loans | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Total Past Due	32,330	19,244
Current	675,499	416,561
(Discount)/ Premium	(41,364)	(38,007)
Total Loans and Leases	666,465	397,798
Acquired Loans | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	0	0
Total Past Due	1	23
Current	10	96
(Discount)/ Premium	154	84
Total Loans and Leases	165	203
Acquired Loans | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	1,353	336
Total Past Due	10,959	4,020
Current	596,298	201,958
(Discount)/ Premium	(12,934)	(4,405)
Total Loans and Leases	594,323	201,573
Acquired Loans | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non- Accrual	1,353	336
Total Past Due	50,570	26,948
Current	1,413,193	692,094
(Discount)/ Premium	(52,988)	(40,326)
Total Loans and Leases	1,410,775	678,716
30-89 Days Past Due | Originated Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	62,146	59,850
30-89 Days Past Due | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,273	8,452
30-89 Days Past Due | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,948	16,019
30-89 Days Past Due | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,382	973
30-89 Days Past Due | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	83	398
30-89 Days Past Due | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	18,686	25,842
30-89 Days Past Due | Originated Loans and Leases | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,192	10,573
30-89 Days Past Due | Originated Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14,096	10,594
30-89 Days Past Due | Originated Loans and Leases | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,313	9,312
30-89 Days Past Due | Originated Loans and Leases | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,859	3,529
30-89 Days Past Due | Originated Loans and Leases | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	43,460	34,008
30-89 Days Past Due | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66,926	24,210
30-89 Days Past Due | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	34,928	9,501
30-89 Days Past Due | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,187	1,789
30-89 Days Past Due | Acquired Loans | Total commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	38,115	11,290
30-89 Days Past Due | Acquired Loans | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,267	2,317
30-89 Days Past Due | Acquired Loans | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17,191	8,428
30-89 Days Past Due | Acquired Loans | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	19
30-89 Days Past Due | Acquired Loans | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,353	2,156
30-89 Days Past Due | Acquired Loans | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	28,811	12,920
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,121	9,113
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1	1
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3	3
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	41	1
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	153	83
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	198	88
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,466	4,386
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,832	3,014
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	611	513
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,014	1,112
≥ 90 Days Past Due and Still Accruing | Originated Loans and Leases | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,923	9,025
≥ 90 Days Past Due and Still Accruing | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	89,950	40,524
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	63,092	23,890
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,452	2,942
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Total commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	69,544	26,832
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Direct installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,013	1,344
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,139	10,816
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Indirect installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1	4
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Consumer lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,253	1,528
≥ 90 Days Past Due and Still Accruing | Acquired Loans | Total consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 20,406	$ 13,692