Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	$ 2,056,120	$ 1,636,526
Securities Available For Sale, Gross Unrealized Gains	23,914	7,394
Securities Available For Sale, Gross Unrealized Losses	(2,418)	(13,353)
Securities Available For Sale, Fair Value	2,077,616	1,630,567
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	29,839	29,738
Securities Available For Sale, Gross Unrealized Gains	165	58
Securities Available For Sale, Fair Value	30,004	29,796
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	382,570	368,463
Securities Available For Sale, Gross Unrealized Gains	2,106	856
Securities Available For Sale, Gross Unrealized Losses	(39)	(1,325)
Securities Available For Sale, Fair Value	384,637	367,994
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,039,245	703,069
Securities Available For Sale, Gross Unrealized Gains	17,406	4,594
Securities Available For Sale, Gross Unrealized Losses		(2,832)
Securities Available For Sale, Fair Value	1,056,651	704,831
Securities Available For Sale, Fair Value	1,056,651
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	552,974	503,328
Securities Available For Sale, Gross Unrealized Gains	3,517	1,032
Securities Available For Sale, Gross Unrealized Losses	(1,768)	(8,530)
Securities Available For Sale, Fair Value	554,723	495,830
Securities Available For Sale, Fair Value	554,723
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	934	1,177
Securities Available For Sale, Gross Unrealized Gains	1	13
Securities Available For Sale, Fair Value	935	1,190
Securities Available For Sale, Fair Value	935
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	2,817	4,299
Securities Available For Sale, Gross Unrealized Losses	(1)	(12)
Securities Available For Sale, Fair Value	2,816	4,287
Securities Available For Sale, Fair Value	2,816
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	36,963	10,748
Securities Available For Sale, Gross Unrealized Gains	205	309
Securities Available For Sale, Gross Unrealized Losses	(30)
Securities Available For Sale, Fair Value	37,138	11,057
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	9,803	14,729
Securities Available For Sale, Gross Unrealized Gains	122	208
Securities Available For Sale, Gross Unrealized Losses	(580)	(651)
Securities Available For Sale, Fair Value	9,345	14,286
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	2,055,145	1,635,551
Securities Available For Sale, Gross Unrealized Gains	23,522	7,070
Securities Available For Sale, Gross Unrealized Losses	(2,418)	(13,350)
Securities Available For Sale, Fair Value	2,076,249	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	392	324
Securities Available For Sale, Gross Unrealized Losses		(3)
Securities Available For Sale, Fair Value	1,367	$ 1,296
Securities Available For Sale, Fair Value	$ 1,367

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)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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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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