Derivatives and Hedging Activities (Details) - USD ($)			3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 09, 2015	Feb. 03, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2017	Dec. 31, 2015
Derivative instruments and hedging activities disclosures
Amount of gain (loss) recorded in accumulated other comprehensive income			$ 824,000	$ (2,947,000)	$ (3,597,000)	$ (3,807,000)
Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Earnings related to derivatives due to hedge ineffectiveness			0	0	0	0
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Amount borrowed under term loan or revolving credit facility	$ 75,000,000	$ 100,000,000
Term of loan facility	5 years	5 years
Derivative, Fixed Interest Rate	2.93%	3.23%
Amount of gain (loss) recorded in accumulated other comprehensive income			(800,000)	2,900,000	(3,600,000)	(3,800,000)
Amount reclassified to interest expense			400,000	$ 600,000	1,300,000	$ 1,400,000
Amount recognized in unearned revenue, prepaid rent and other liabilities			$ 3,000,000		$ 3,000,000			$ 800,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging | Forecast
Derivative instruments and hedging activities disclosures
Amount estimated to be reclassified as an increase to interest expense							$ 1,700,000
LIBOR | Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Reference rate	one-month LIBOR