Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Abstract]
Cash on deposit with Federal Reserve Bank	$ 631,562	$ 392,413
Compensating balances with Federal Reserve Bank	7,507us-gaap_CompensatingBalanceAmount	1,412us-gaap_CompensatingBalanceAmount
Loans and Leases Receivable Disclosure [Abstract]
Mortgage loans held for sale	40,828us-gaap_LoansHeldForSaleMortgages	40,861us-gaap_LoansHeldForSaleMortgages
Impairment losses	102	616	70
Write-downs of OREO	224us-gaap_ImpairmentOfRealEstate	3,512us-gaap_ImpairmentOfRealEstate	6,724us-gaap_ImpairmentOfRealEstate
Federal Home Loan Bank Stock and Federal Reserve Bank Stock [Abstract]
Federal Reserve Bank stock	16,187us-gaap_FederalReserveBankStock	13,357us-gaap_FederalReserveBankStock
Federal Home Loan Bank stock	10,662us-gaap_FederalHomeLoanBankStock	7,003us-gaap_FederalHomeLoanBankStock
Advertising expense	3,734us-gaap_AdvertisingExpense	3,532us-gaap_AdvertisingExpense	3,555us-gaap_AdvertisingExpense
Share-based Compensation [Abstract]
Stock compensation expense	3,014	2,936	2,485
Tax benefits from stock-based compensation	$ 1,153	$ 1,122	$ 950

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