Credit Facility (Details) (Credit facility, USD $)	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Credit Facility
Maximum borrowing capacity	$ 65,000,000	$ 60,000,000
Variable interest rate base	LIBOR
Percentage points added to the reference rate	2.75%
Outstanding borrowings	52,500,000		58,500,000
Weighted average interest rate on the amount outstanding (as a percent)	2.93%
Amount available for borrowing pursuant to the facility	$ 12,500,000
Minimum
Credit Facility
Percentage points added to the reference rate	1.50%
Maximum
Credit Facility
Percentage points added to the reference rate	3.50%