Derivatives Instrument and Hedging Activities (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) item	Mar. 31, 2015 USD ($)	Dec. 31, 2015 item
Derivatives Instrument and Hedging Activities
Interest paid	$ 2,679,000	$ 15,815,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivatives Instrument and Hedging Activities
Number of agreements | item	1		1
Notional amount	$ 200,000,000
Fixed interest rate (as a percent)	1.6775%
Interest paid	$ 658,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging | Interest expense.
Derivatives Instrument and Hedging Activities
Increase to interest expense	$ 1,500,000