Basis of Presentation - Leases (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 01, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 17,700,000		$ 17,700,000
Operating lease, liability		23,705,000		23,705,000
Operating lease, lease income		700,000		1,300,000
Lessor, lease, cost		$ 0	$ 1,500,000	$ 0	$ 2,700,000
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 24,600,000
Operating lease, liability	24,600,000
Ground Leases | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in operating lease, right-of-use asset	5,500,000
Decrease in operating lease, liability	$ 5,500,000