Securities Purchased under Resale Agreements and Sold under Repurchase Agreements (Details 2) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets, Resale Agreements
Gross Amounts of Recognized Assets	$ 1,700,000	$ 2,100,000
Gross Amounts Offset on the Consolidated Balance Sheets	(400,000)	(100,000)
Net Amounts of Assets Presented on the Consolidated Balance Sheets	1,300,000	2,000,000
Gross Amounts Not Offset on the Consolidated Balance Sheets
Financial Instruments	0	(150,000)
Collateral Pledged	(1,291,869)	(1,839,120)
Net Amount	8,131	10,880
Liabilities, Repurchase Agreements
Gross Amounts of Recognized Liabilities	450,000	450,000
Gross Amounts Offset on the Consolidated Balance Sheets	(400,000)	(100,000)
Net Amounts of Liabilities Presented on the Consolidated Balance Sheets	50,000	350,000
Gross Amounts Not Offset on the Consolidated Balance Sheets
Financial Instruments	0	(150,000)
Collateral Posted	(50,000)	(200,000)
Net Amount	$ 0	$ 0