Volume of Activity for Interest Rate Derivative Instruments (Details) (Interest Rate Swap, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Interest Rate Swap
Derivative [Line Items]
Notional amount, beginning of period	$ 10,700,000	$ 10,700,000
Additions	0	600,000
Expirations and terminations	(600,000)	(200,000)
Notional amount, end of period	$ 10,100,000	$ 11,100,000