Securities - Amortized Cost and Fair Value of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 1,640,299	$ 1,408,780
Securities available for sale, Gross Unrealized Gains	29,161	25,366
Securities available for sale, Gross Unrealized Losses	7,050	12,374
Securities Available for Sale, Fair Value	1,662,410	1,421,772
U.S. Treasury and government agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	300,257	504
Securities available for sale, Gross Unrealized Gains	446	2
Securities available for sale, Gross Unrealized Losses	1	1
Securities Available for Sale, Fair Value	300,702	505
Municipal obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	18,495	35,809
Securities available for sale, Gross Unrealized Gains	272	177
Securities available for sale, Gross Unrealized Losses		25
Securities Available for Sale, Fair Value	18,767	35,961
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, Gross Unrealized Gains
Securities available for sale, Gross Unrealized Losses
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	8,784	9,965
Securities available for sale, Gross Unrealized Gains	877	785
Securities available for sale, Gross Unrealized Losses	1	27
Securities Available for Sale, Fair Value	9,660	10,723
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,218,982	1,262,633
Securities available for sale, Gross Unrealized Gains	27,566	24,402
Securities available for sale, Gross Unrealized Losses	5,325	10,077
Securities Available for Sale, Fair Value	1,241,223	1,276,958
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	90,281	96,369
Securities available for sale, Gross Unrealized Gains
Securities available for sale, Gross Unrealized Losses	1,723	2,244
Securities Available for Sale, Fair Value	$ 88,558	$ 94,125

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)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Section 50

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 45

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- Definition

Amount before tax of unrealized gain 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

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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- Definition

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

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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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