Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 3,836,877	$ 2,892,522
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Pass
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 3,653,344	$ 2,780,315
Total percentage of recorded investment in commercial loan	95.20%	96.10%
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 83,680	$ 65,968
Total percentage of recorded investment in commercial loan	2.20%	2.30%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 99,853	$ 46,239
Total percentage of recorded investment in commercial loan	2.60%	1.60%
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 2,166,603	$ 1,682,236
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 2,094,851	$ 1,635,132
Total percentage of recorded investment in commercial loan	96.70%	97.20%
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 19,938	$ 23,597
Total percentage of recorded investment in commercial loan	0.90%	1.40%
Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 51,814	$ 23,507
Total percentage of recorded investment in commercial loan	2.40%	1.40%
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 1,256,830	$ 994,138
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial and Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 1,182,685	$ 948,663
Total percentage of recorded investment in commercial loan	94.10%	95.40%
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 43,896	$ 30,357
Total percentage of recorded investment in commercial loan	3.50%	3.10%
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 30,249	$ 15,118
Total percentage of recorded investment in commercial loan	2.40%	1.50%
Commercial Construction
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 413,444	$ 216,148
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 375,808	$ 196,520
Total percentage of recorded investment in commercial loan	90.90%	90.90%
Commercial Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 19,846	$ 12,014
Total percentage of recorded investment in commercial loan	4.80%	5.60%
Commercial Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 17,790	$ 7,614
Total percentage of recorded investment in commercial loan	4.30%	3.50%