Investments (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 1,522,871	$ 1,500,516
Available-for-sale Securities, Gross Unrealized Gain	47,908	27,774
Available-for-sale Securities, Gross Unrealized Loss	(3,602)	(33,545)
Securities available‑for‑sale	1,567,177us-gaap_AvailableForSaleSecurities	1,494,745us-gaap_AvailableForSaleSecurities
Government agency and government-sponsored enterprise pass through securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	515,902	691,944
Available-for-sale Securities, Gross Unrealized Gain	20,142	18,012
Available-for-sale Securities, Gross Unrealized Loss	(372)	(2,768)
Government agency and government-sponsored enterprise collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	275,513	197,069
Available-for-sale Securities, Gross Unrealized Gain	3,513	388
Available-for-sale Securities, Gross Unrealized Loss	(1,080)	(4,584)
Covered private label collateralized mortgage obligation [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	26,889	30,502
Available-for-sale Securities, Gross Unrealized Gain	7,153	7,552
Available-for-sale Securities, Gross Unrealized Loss	(95)	(150)
Other Private Label Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	10,961	0
Available-for-sale Securities, Gross Unrealized Gain	46	0
Available-for-sale Securities, Gross Unrealized Loss	(93)	0
Securities available‑for‑sale		0
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	521,499	459,182
Available-for-sale Securities, Gross Unrealized Gain	15,899	1,749
Available-for-sale Securities, Gross Unrealized Loss	(1,282)	(24,273)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	110,074	84,119
Available-for-sale Securities, Gross Unrealized Gain	597	71
Available-for-sale Securities, Gross Unrealized Loss	(562)	(1,483)
US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	36,232	10,046
Available-for-sale Securities, Gross Unrealized Gain	525	0
Available-for-sale Securities, Gross Unrealized Loss	0	(174)
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	25,801	27,654
Available-for-sale Securities, Gross Unrealized Gain	33	2
Available-for-sale Securities, Gross Unrealized Loss	$ (118)	$ (113)

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

-Topic 320

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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

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ 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

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