Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 2,660,260	$ 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	2,492,199	2,430,926
Total percentage of recorded investment in commercial loan	93.70%	93.70%
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	113,620	106,779
Total percentage of recorded investment in commercial loan	4.20%	4.10%
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	54,441	56,175
Total percentage of recorded investment in commercial loan	2.10%	2.20%
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	1,607,958	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	1,520,208	1,519,720
Total percentage of recorded investment in commercial loan	94.60%	94.50%
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	56,618	57,073
Total percentage of recorded investment in commercial loan	3.50%	3.60%
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	31,132	30,963
Total percentage of recorded investment in commercial loan	1.90%	1.90%
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	884,870	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	828,092	792,029
Total percentage of recorded investment in commercial loan	93.60%	94.00%
Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	41,572	34,085
Total percentage of recorded investment in commercial loan	4.70%	4.10%
Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	15,206	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	167,432	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	143,899	119,177
Total percentage of recorded investment in commercial loan	85.90%	82.90%
Commercial Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	15,430	15,621
Total percentage of recorded investment in commercial loan	9.20%	10.90%
Commercial Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in commercial loan	$ 8,103	$ 8,877
Total percentage of recorded investment in commercial loan	4.90%	6.20%