Volume of Activity for Interest Rate Derivative Instruments (Details) (Interest Rate Swap, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Interest Rate Swap
Derivative [Line Items]
Notional amount as of December 31, 2012	$ 10,700,000
Additions	800,000
Settlements, terminations, or expirations	(1,000,000)
Notional amount as of December 31, 2013	$ 10,500,000