Securities - Amortized Cost and Fair Value of Available for Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	$ 2,086,745	$ 1,631,761
Securities available for sale, Gross Unrealized Gains	20,120	32,543
Securities available for sale, Gross Unrealized Losses	13,461	4,139
Securities Available for Sale, Fair Value	2,093,404	1,660,165
U.S. Treasury and Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	135	300,207
Securities available for sale, Gross Unrealized Gains		372
Securities available for sale, Gross Unrealized Losses	1	71
Securities Available for Sale, Fair Value	134	300,508
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	39,410	13,995
Securities available for sale, Gross Unrealized Gains	235	186
Securities available for sale, Gross Unrealized Losses	38	5
Securities Available for Sale, Fair Value	39,607	14,176
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	3,500	3,500
Securities Available for Sale, Fair Value	3,500	3,500
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	2,447	8,673
Securities available for sale, Gross Unrealized Gains	358	891
Securities available for sale, Gross Unrealized Losses	48	11
Securities Available for Sale, Fair Value	2,757	9,553
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	1,750,168	1,217,293
Securities available for sale, Gross Unrealized Gains	19,387	31,094
Securities available for sale, Gross Unrealized Losses	11,182	2,823
Securities Available for Sale, Fair Value	1,758,373	1,245,564
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, Amortized Cost	291,085	88,093
Securities available for sale, Gross Unrealized Gains	140
Securities available for sale, Gross Unrealized Losses	2,192	1,229
Securities Available for Sale, Fair Value	$ 289,033	$ 86,864

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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