Term Loans (Details) - USD ($)	1 Months Ended		9 Months Ended
	Jun. 30, 2015	Jan. 31, 2013	Sep. 30, 2017	Dec. 31, 2016
Term Loans
Term loans, net			$ 319,347,000	$ 319,127,000
Senior Unsecured Term Loans
Term Loans
Deferred finance costs			653,000	$ 873,000
Senior Unsecured Term Loans | $250 million senior unsecured term loan
Term Loans
Term loans, net	$ 250,000,000
Variable reference rate	one-month LIBOR
Variable interest rate, basis points spread over variable reference rate (as a percent)	0.95%
Deferred financing costs incurred			1,200,000
Senior Unsecured Term Loans | Interest rate swaps | $250 million senior unsecured term loan
Term Loans
Effective yield (as a percent)	2.67%
Senior Unsecured Term Loans | ARCT | $70 million senior unsecured term loan
Term Loans
Term loans, net		$ 70,000,000
Variable reference rate		one-month LIBOR
Variable interest rate, basis points spread over variable reference rate (as a percent)		1.20%
Deferred financing costs incurred			$ 303,000
Senior Unsecured Term Loans | ARCT | Interest rate swaps | $70 million senior unsecured term loan
Term Loans
Effective yield (as a percent)		2.15%