Investment Securities - Summary of Interest Income Earned on Investment Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Total investment income	$ 72,208	$ 68,378	$ 50,399
Investment securities available-for-sale [Member]
Net Investment Income [Line Items]
Taxable	48,854	47,301	28,186
Tax-advantaged	14,336	20,913	22,025
Investment securities held-to-maturity [Member]
Net Investment Income [Line Items]
Taxable	4,451	164	188
Tax-advantaged	$ 4,567	$ 0	$ 0

Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2,3)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24721-111560

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to tax benefits. Excludes operating interest income on securities exempt from state, federal and other income tax.

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

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