Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	$ 2,659,080	$ 2,260,021
Securities Available For Sale, Gross Unrealized Gains	4,833	4,172
Securities Available For Sale, Gross Unrealized Losses	(25,098)	(32,206)
Securities Available For Sale, Fair Value	2,638,815	2,231,987
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	29,908	29,874
Securities Available For Sale, Gross Unrealized Gains	37	79
Securities Available For Sale, Fair Value	29,945	29,953
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	397,634	367,604
Securities Available For Sale, Gross Unrealized Gains	676	864
Securities Available For Sale, Gross Unrealized Losses	(3,104)	(3,370)
Securities Available For Sale, Fair Value	395,206	365,098
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,650,743	1,267,535
Securities Available For Sale, Gross Unrealized Gains	3,024	2,257
Securities Available For Sale, Gross Unrealized Losses	(10,753)	(16,994)
Securities Available For Sale, Fair Value	1,643,014	1,252,798
Securities Available For Sale, Fair Value	1,643,014
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	514,232	546,659
Securities Available For Sale, Gross Unrealized Gains	347	419
Securities Available For Sale, Gross Unrealized Losses	(10,616)	(11,104)
Securities Available For Sale, Fair Value	503,963	535,974
Securities Available For Sale, Fair Value	503,963
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	2	891
Securities Available For Sale, Gross Unrealized Gains		6
Securities Available For Sale, Fair Value	2	897
Securities Available For Sale, Fair Value	2
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	420	1,292
Securities Available For Sale, Gross Unrealized Losses	(1)	(1)
Securities Available For Sale, Fair Value	419	1,291
Securities Available For Sale, Fair Value	419
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	34,763	36,065
Securities Available For Sale, Gross Unrealized Gains	69	86
Securities Available For Sale, Gross Unrealized Losses	(154)	(302)
Securities Available For Sale, Fair Value	34,678	35,849
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	21,899	9,828
Securities Available For Sale, Gross Unrealized Gains	68	94
Securities Available For Sale, Gross Unrealized Losses	(373)	(435)
Securities Available For Sale, Fair Value	21,594	9,487
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	2,649,601	2,259,748
Securities Available For Sale, Gross Unrealized Gains	4,221	3,805
Securities Available For Sale, Gross Unrealized Losses	(25,001)	(32,206)
Securities Available For Sale, Fair Value	2,628,821	2,231,347
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	9,479	273
Securities Available For Sale, Gross Unrealized Gains	612	367
Securities Available For Sale, Gross Unrealized Losses	(97)
Securities Available For Sale, Fair Value	9,994	$ 640
Securities Available For Sale, Fair Value	$ 9,994

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 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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