Lease Agreements - Company as Lessee - Narrative and Components of Leases (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Office lease, renewal term		5 years
Operating lease right-of-use assets	$ 75,478	$ 75,478	$ 0
Total leased assets	75,478	75,478
Operating lease liabilities	77,495	77,495
Total lease liabilities	77,495	77,495
Lease, Cost [Abstract]
Operating lease cost	1,686	5,059
Variable lease cost	109	622
Short-term lease cost	171	455
Sublease income	(109)	(326)
Total lease cost	1,857	5,810
Operating lease right-of-use assets
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	75,478	75,478
Operating lease liabilities
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 77,495	$ 77,495
Minimum
Lessee, Lease, Description [Line Items]
Office lease term of contract		5 years
Ground lease term		20 years
Ground lease, renewal term		10 years
Maximum
Lessee, Lease, Description [Line Items]
Office lease term of contract		10 years
Ground lease term		85 years
Ground lease, renewal term		39 years