Loans and Allowance for Losses and Concentrations of Credit Risk - Certain Loans Acquired Delinquencies and Net Credit Losses (Details) (USD $)	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 87,963,000			$ 95,041,000
Net credit losses (recoveries)	(21,000)		2,857,000
Loans and leases receivable, impaired, loans past due period, minimum	90 days
On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses (recoveries)	(21,000)		2,857,000
On-balance sheet [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses (recoveries)	(21,000)		2,857,000
Off-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses (recoveries)	0		0
Off-balance sheet [Member] | Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net credit losses (recoveries)	0		0
90-day delinquencies [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	25,911,000			28,296,000
90-day delinquencies [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	1,200,000	[1]		1,200,000	[1]
90-day delinquencies [Member] | On-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	25,118,000			27,580,000
90-day delinquencies [Member] | On-balance sheet [Member] | Eligible Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	25,118,000	[1]		27,580,000	[1]
90-day delinquencies [Member] | Off-balance sheet [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	793,000			716,000
90-day delinquencies [Member] | Off-balance sheet [Member] | Long-Term Standby Purchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Unpaid Principal Balance	$ 793,000			$ 716,000

[1] Includes loans and loans underlying off-balance sheet Farm & Ranch Guaranteed Securities and LTSPCs that are 90 days or more past due, in foreclosure, restructured after delinquency, or in bankruptcy, excluding loans performing under either their original loan terms or a court-approved bankruptcy plan.