Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	$ 2,107,479	$ 1,636,526
Securities Available For Sale, Gross Unrealized Gains	28,561	7,394
Securities Available For Sale, Gross Unrealized Losses	(2,378)	(13,353)
Securities Available For Sale, Fair Value	2,133,662	1,630,567
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	29,805	29,738
Securities Available For Sale, Gross Unrealized Gains	257	58
Securities Available For Sale, Fair Value	30,062	29,796
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	432,534	368,463
Securities Available For Sale, Gross Unrealized Gains	3,235	856
Securities Available For Sale, Gross Unrealized Losses		(1,325)
Securities Available For Sale, Fair Value	435,769	367,994
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,095,826	703,069
Securities Available For Sale, Gross Unrealized Gains	19,051	4,594
Securities Available For Sale, Gross Unrealized Losses		(2,832)
Securities Available For Sale, Fair Value	1,114,877	704,831
Securities Available For Sale, Fair Value	1,114,877
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	495,943	503,328
Securities Available For Sale, Gross Unrealized Gains	5,239	1,032
Securities Available For Sale, Gross Unrealized Losses	(1,535)	(8,530)
Securities Available For Sale, Fair Value	499,647	495,830
Securities Available For Sale, Fair Value	499,647
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,034	1,177
Securities Available For Sale, Gross Unrealized Gains		13
Securities Available For Sale, Gross Unrealized Losses	(56)
Securities Available For Sale, Fair Value	978	1,190
Securities Available For Sale, Fair Value	978
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	3,389	4,299
Securities Available For Sale, Gross Unrealized Gains	4
Securities Available For Sale, Gross Unrealized Losses		(12)
Securities Available For Sale, Fair Value	3,393	4,287
Securities Available For Sale, Fair Value	3,393
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	38,195	10,748
Securities Available For Sale, Gross Unrealized Gains	280	309
Securities Available For Sale, Gross Unrealized Losses	(27)
Securities Available For Sale, Fair Value	38,448	11,057
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	9,778	14,729
Securities Available For Sale, Gross Unrealized Gains	150	208
Securities Available For Sale, Gross Unrealized Losses	(760)	(651)
Securities Available For Sale, Fair Value	9,168	14,286
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	2,106,504	1,635,551
Securities Available For Sale, Gross Unrealized Gains	28,216	7,070
Securities Available For Sale, Gross Unrealized Losses	(2,378)	(13,350)
Securities Available For Sale, Fair Value	2,132,342	1,629,271
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	975	975
Securities Available For Sale, Gross Unrealized Gains	345	324
Securities Available For Sale, Gross Unrealized Losses		(3)
Securities Available For Sale, Fair Value	1,320	$ 1,296
Securities Available For Sale, Fair Value	$ 1,320

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

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

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