Balance Sheet Offsetting (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Reverse repurchase agreements
Gross Amount Recognized	$ 700,462,000	$ 200,000,000
Gross Amount Offset	(500,156,000)
Net Amount Presented in the Balance Sheet	200,306,000	200,000,000
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(200,000,000)	(200,000,000)
Net Amount	306,000
Repurchase agreements
Gross Amount Recognized	500,156,000
Gross Amount Offset	(500,156,000)
Derivatives not designated as hedging instruments | Securities swaps
Financial instruments that are eligible for offset
Principal amount of collateral swap agreement	500,000,000
Financial assets
Fair Value of Securities Pledged as Collateral	531,000,000
Financial liabilities
Fair Value of Securities Received as Collateral	526,500,000
Derivatives not designated as hedging instruments | Master netting arrangements and similar agreements
Financial assets
Gross Amount Recognized	10,838,000	18,749,000
Gross Amount Offset	(5,318,000)	(13,323,000)
Net Amount Presented in the Balance Sheet	5,520,000	5,426,000
Net Amount	5,520,000	5,426,000
Financial liabilities
Gross Amount Recognized	39,432,000	32,193,000
Gross Amount Offset	(5,318,000)	(13,323,000)
Net Amount Presented in the Balance Sheet	34,114,000	18,870,000
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(11,684,000)	(12,376,000)
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral	(17,707,000)	(7,761,000)
Net Amount	4,723,000	(1,267,000)
Total financial assets and total financial liabilities | Master netting arrangements and similar agreements
Financial assets
Gross Amount Recognized	711,300,000	218,749,000
Gross Amount Offset	(505,474,000)	(13,323,000)
Net Amount Presented in the Balance Sheet	205,826,000	205,426,000
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(200,000,000)	(200,000,000)
Net Amount	5,826,000	5,426,000
Financial Liabilities
Gross Amount Recognized	539,588,000	32,193,000
Gross Amount Offset	(505,474,000)	(13,323,000)
Net Amount Presented in the Balance Sheet	34,114,000	18,870,000
Gross Amounts Not Offset in the Balance Sheet, Securities Collateral	(11,684,000)	(12,376,000)
Gross Amounts Not Offset in the Balance Sheet, Cash Collateral	(17,707,000)	(7,761,000)
Net Amount	$ 4,723,000	$ (1,267,000)