Amounts Incurred for Management Fee and Reimbursable Expenses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Management fee									$ 16,235	$ 16,532	$ 18,180
Total	$ 4,020	$ 4,037	$ 4,083	$ 4,095	$ 4,112	$ 4,122	$ 4,144	$ 4,154
Share-based compensation	$ 1,211	$ 966	$ 1,034	$ 1,045	$ 1,020	$ 890	$ 842	$ 860	4,256	3,612	2,594
Management Fees
Related Party Transaction [Line Items]
Management fee									16,235	16,532	18,180
Reimbursable expenses									5,110	4,239	3,200
Total									21,345	20,771	21,380
Share-based compensation									$ 4,256	$ 3,612	$ 2,594