Basis of Presentation and Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating segments | segment	1
Cumulative effect adjustment to accumulated deficit		$ (40,310)		$ 9,229
Operating lease assets	$ 60,573		$ 61,674
Total operating lease liabilities	$ 71,004
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit		(40,310)		$ 33,349
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected future increase (decrease) in operating expenses		(26,000)
Expected future increase (decrease) in interest expense		13,000
Operating lease assets		$ 61,674	61,700
Total operating lease liabilities			71,900
Accounting Standards Update 2016-02 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment to accumulated deficit			$ 40,300
Fan Pier Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Length of lease					15 years