Repurchase Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase, Gross	$ 622,182	$ 324,426
Securities Sold under Agreements to Repurchase	622,182	324,426
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	722,000	418,300
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	592,182	294,426
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	30,000	30,000
Government Agency
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	4,276	6,914
Government Agency | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Government Agency | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Government Agency | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Government Agency | Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	4,276	6,914
U. S. Treasury
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	617,906	186,011
U. S. Treasury | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	592,182	162,925
U. S. Treasury | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
U. S. Treasury | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	0	0
U. S. Treasury | Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	$ 25,724	23,086
Mortgage Backed Securities, Other
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		131,501
Mortgage Backed Securities, Other | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		131,501
Mortgage Backed Securities, Other | Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		0
Mortgage Backed Securities, Other | 30 - 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		0
Mortgage Backed Securities, Other | Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase		$ 0