Volume of Activity for Interest Rate Derivative Instruments (Details) (Interest Rate Swap, USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Interest Rate Swap
Derivative [Line Items]
Notional Value, Beginning of period	$ 10,500,000	$ 10,700,000
Additions	0	800,000
Expirations and terminations	(600,000)	(400,000)
Notional Value, End of period	$ 9,900,000	$ 11,100,000