Derivatives and Hedging Activities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Net gain (loss) related to derivative instrument	$ 6,281,000	$ (4,112,000)	$ 22,636,000	$ (4,746,000)
Ineffective portion of the change in fair value derivatives			$ 0
Interest Rate Swaps
Derivative [Line Items]
Weighted average fixed rate	1.844%		1.844%
Notional amount	$ 1,200,000,000		$ 1,200,000,000
Interest expense	(100,000)	$ 2,600,000	800,000	$ 5,300,000
Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Fair value of derivative instruments	$ 33,700,000		$ 33,700,000		$ 11,300,000