Lease Agreements - Company as Lessee - Narrative and Components of Leases (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Office lease, renewal term		5 years
Operating lease right-of-use assets	$ 76,205	$ 76,205	$ 0
Total leased assets	76,205	76,205
Operating lease liabilities	78,226	78,226
Total lease liabilities	78,226	78,226
Lease, Cost [Abstract]
Operating lease cost	1,687	3,373
Variable lease cost	371	513
Short-term lease cost	152	284
Sublease income	(110)	(217)
Total lease cost	2,100	3,953
Operating lease right-of-use assets
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	76,205	76,205
Operating lease liabilities
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 78,226	$ 78,226
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