Loans and Leases - Summary of Commercial Loans and Leases by Credit Quality (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	$ 20,998,766	$ 14,896,943
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	8,741,864	5,435,162
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	4,170,667	3,042,781
Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	266,720	196,636
Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	17,063	35,878
Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	13,196,314	8,710,457
Originated Loans and Leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	15,345,490	12,547,987
Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	5,174,783	4,095,817
Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,495,247	2,711,886
Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	266,720	196,636
Originated Loans and Leases | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	17,063	35,878
Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	8,953,813	7,040,217
Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	5,653,276	2,348,956
Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,567,081	1,339,345
Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	675,420	330,895
Acquired Loans | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	0	0
Acquired Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	0	0
Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	4,242,501	1,670,240
Pass | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	4,922,872	3,895,764
Pass | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,266,966	2,475,955
Pass | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	260,235	188,662
Pass | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	15,866	34,531
Pass | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	8,465,939	6,594,912
Pass | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,102,788	1,144,676
Pass | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	603,611	274,819
Pass | Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,706,399	1,419,495
Special Mention | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	152,744	130,452
Special Mention | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	132,975	104,652
Special Mention | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	4,425	3,789
Special Mention | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	43	264
Special Mention | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	290,187	239,157
Special Mention | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	250,987	85,894
Special Mention | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	26,059	20,593
Special Mention | Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	277,046	106,487
Substandard | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	98,728	69,588
Substandard | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	92,091	128,089
Substandard | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	2,060	4,185
Substandard | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	1,154	1,083
Substandard | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	194,033	202,945
Substandard | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	213,089	108,128
Substandard | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	45,661	34,967
Substandard | Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	258,750	143,095
Doubtful | Originated Loans and Leases | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	439	13
Doubtful | Originated Loans and Leases | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,215	3,190
Doubtful | Originated Loans and Leases | Commercial leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	0	0
Doubtful | Originated Loans and Leases | Other
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	0	0
Doubtful | Originated Loans and Leases | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	3,654	3,203
Doubtful | Acquired Loans | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	217	647
Doubtful | Acquired Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	89	516
Doubtful | Acquired Loans | Total commercial loans and leases
Financing Receivable, Recorded Investment [Line Items]
Total commercial loans and leases	$ 306	$ 1,163