Bank Loans (Details) (USD $)	3 Months Ended		3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Maximum [Member]	Mar. 31, 2014 Minimum [Member]	Mar. 31, 2014 Term Loan Agreement [Member]	Dec. 31, 2013 Term Loan Agreement [Member]	Dec. 20, 2011 Term Loan Agreement [Member]	Mar. 31, 2014 Term Loan Agreement [Member] Maximum [Member]	Mar. 31, 2014 Term Loan Agreement [Member] Minimum [Member]	Apr. 28, 2014 Subsequent Event [Member]
Line of Credit Facility [Line Items]
Credit Facility, borrowing limit	$ 250,000,000
Credit Facility, frequency of interest payment	monthly
Spread over LIBOR			1.70%	0.875%		1.20%		2.25%	1.15%	0.925%
Previous spread over LIBOR	1.10%
Credit Facility, percentage of commitment fees	0.15%		0.30%	0.125%
Credit Facility, amount outstanding	0	0
Unsecured debt							250,000,000
Unamortized commitments fees	$ 408,000	$ 485,000
Length of debt term (in years)					3 years
Term loan, maturity date					Dec. 31, 2014
Term loan, repayment date					Nov. 01, 2013