Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 2,746,885	$ 2,593,880
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	2,603,835	2,430,926
Total percentage of recorded investment in commercial loan	94.80%	93.70%
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	92,123	106,779
Total percentage of recorded investment in commercial loan	3.40%	4.10%
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	50,927	56,175
Total percentage of recorded investment in commercial loan	1.80%	2.20%
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	1,636,383	1,607,756
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	1,563,882	1,519,720
Total percentage of recorded investment in commercial loan	95.60%	94.50%
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	45,275	57,073
Total percentage of recorded investment in commercial loan	2.80%	3.60%
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	27,226	30,963
Total percentage of recorded investment in commercial loan	1.60%	1.90%
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	922,191	842,449
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	872,686	792,029
Total percentage of recorded investment in commercial loan	94.60%	94.00%
Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	33,966	34,085
Total percentage of recorded investment in commercial loan	3.70%	4.10%
Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	15,539	16,335
Total percentage of recorded investment in commercial loan	1.70%	1.90%
Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	188,311	143,675
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	167,267	119,177
Total percentage of recorded investment in commercial loan	88.80%	82.90%
Commercial Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	12,882	15,621
Total percentage of recorded investment in commercial loan	6.80%	10.90%
Commercial Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 8,162	$ 8,877
Total percentage of recorded investment in commercial loan	4.40%	6.20%