Term Loan (Details) (USD $)	1 Months Ended	3 Months Ended
	Jan. 31, 2013	Mar. 31, 2015	Dec. 31, 2014
Credit facility
Term loan		$ 70,000,000	$ 70,000,000
Senior unsecured term loan
Credit facility
Term loan	70,000,000
Variable reference rate	one month LIBOR
Variable interest rate, basis points spread over variable reference rate (as a percent)	1.20%
Maximum interest rate (as a percent)	2.15%
Deferred financing costs incurred		303,000
Deferred finance costs		$ 172,000	$ 187,000