Arbitrage Trading Account (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Trading Securities and Derivative Instruments [Abstract]
Arbitrage trading account	$ 522,128,000	$ 329,077,000
Options Held | Long
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	2,000,000
Derivative, notional amount	28,000,000
Options Held | Short
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	2,000,000
Derivative, notional amount	$ 22,000,000