Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	$ 1,636,526	$ 1,534,771	$ 1,169,482
Securities Available For Sale, Gross Unrealized Gains	7,394	11,215	11,463
Securities Available For Sale, Gross Unrealized Losses	(13,353)	(11,921)	(39,295)
Securities Available For Sale, Fair Value	1,630,567	1,534,065	1,141,650
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	29,738	29,604
Securities Available For Sale, Gross Unrealized Gains	58	78
Securities Available For Sale, Fair Value	29,796	29,682
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	368,463	338,330	336,763
Securities Available For Sale, Gross Unrealized Gains	856	742	126
Securities Available For Sale, Gross Unrealized Losses	(1,325)	(1,939)	(5,904)
Securities Available For Sale, Fair Value	367,994	337,133	330,985
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	703,069	546,572	247,880
Securities Available For Sale, Gross Unrealized Gains	4,594	7,548	4,304
Securities Available For Sale, Gross Unrealized Losses	(2,832)	(35)	(1,303)
Securities Available For Sale, Fair Value	704,831	554,085	250,881
Securities Available For Sale, Fair Value	704,831
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	503,328	580,601	511,098
Securities Available For Sale, Gross Unrealized Gains	1,032	1,617	895
Securities Available For Sale, Gross Unrealized Losses	(8,530)	(9,047)	(20,794)
Securities Available For Sale, Fair Value	495,830	573,171	491,199
Securities Available For Sale, Fair Value	495,830
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,177	1,414	1,747
Securities Available For Sale, Gross Unrealized Gains	13	17	15
Securities Available For Sale, Fair Value	1,190	1,431	1,762
Securities Available For Sale, Fair Value	1,190
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	4,299	7,891
Securities Available For Sale, Gross Unrealized Losses	(12)	(11)
Securities Available For Sale, Fair Value	4,287	7,880
Securities Available For Sale, Fair Value	4,287
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	10,748	12,713	16,842
Securities Available For Sale, Gross Unrealized Gains	309	477	410
Securities Available For Sale, Gross Unrealized Losses		(32)	(250)
Securities Available For Sale, Fair Value	11,057	13,158	17,002
Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost			37,203
Securities Available For Sale, Gross Unrealized Gains			4,507
Securities Available For Sale, Gross Unrealized Losses			(10,115)
Securities Available For Sale, Fair Value			31,595
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	14,729	16,615	16,505
Securities Available For Sale, Gross Unrealized Gains	208	420	524
Securities Available For Sale, Gross Unrealized Losses	(651)	(857)	(929)
Securities Available For Sale, Fair Value	14,286	16,178	16,100
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,635,551	1,533,740	1,168,038
Securities Available For Sale, Gross Unrealized Gains	7,070	10,899	10,781
Securities Available For Sale, Gross Unrealized Losses	(13,350)	(11,921)	(39,295)
Securities Available For Sale, Fair Value	1,629,271	1,532,718	1,139,524
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	975	1,031	1,444
Securities Available For Sale, Gross Unrealized Gains	324	316	682
Securities Available For Sale, Gross Unrealized Losses	(3)
Securities Available For Sale, Fair Value	1,296	$ 1,347	$ 2,126
Securities Available For Sale, Fair Value	$ 1,296

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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