Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Lease renewal term	5 years
Lease termination term	1 year
Operating lease right of use assets	$ 124,723
Operating lease liabilities	149,413
Increase to accumulated deficit	580,581		$ 542,169
Lease not yet commenced	$ 657
Lease not yet commenced, term	10 years
One Lease, Lessor Affiliate of Significant Investor
Lessee, Lease, Description [Line Items]
Operating lease right of use assets	$ 1,521
Operating lease liabilities	1,577
Rental expense	$ 115
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease terms	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease terms	15 years
ASU 2016-02
Lessee, Lease, Description [Line Items]
Operating lease right of use assets		$ 128,890
Operating lease liabilities		153,676
Deferred rent		22,881
Tenant improvements receivable		355
Increase to accumulated deficit		$ 1,550