Revolving Credit Facility (Details) (USD $)										0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Jul. 25, 2013 JPMorgan Chase Bank, N.A. Revolving Credit Facility extension	Sep. 30, 2014 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 31, 2014 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jun. 24, 2014 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Mar. 26, 2014 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Dec. 31, 2013 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Interest Rate, Option Two Base Rate Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Interest Rate, Option Two Base Rate Minimum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Interest Rate, Option One LIBOR Maximum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Interest Rate, Option One LIBOR Minimum JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Base Rate, Option Two Federal Funds Effective Rate JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Line of Credit Facility, Base Rate, Option Three Adjusted LIBOR JPMorgan Chase Bank, N.A. Revolving Credit Facility	Jul. 25, 2013 Above Threshold JPMorgan Chase Bank, N.A.	Jul. 25, 2013 Below Threshold JPMorgan Chase Bank, N.A.
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 50,000,000
Additional borrowing capacity									750,000,000
Increase in additional borrowing capacity						330,000,000	100,000,000
Interest rate										1.20%	0.60%	2.20%	1.60%	0.50%	1.00%
Unused capacity commitment fee																0.25%	0.15%
Commitment fee percentage			50.00%
Credit facility	299,747,000	0		299,700,000	415,000,000
Remaining borrowing capacity				$ 115,300,000				$ 31,100,000
Number of one year extensions			2