Nature of Business and Accounting Policies - Stock-Based Compensation - Improvement (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating loss carryforwards	$ 2,900,000	$ 775,500
Accounting standards update 2016-09, excess tax benefit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating loss carryforwards			$ 410,800
Deferred income tax assets, net			3,400
Accounting standards update 2016-09, forfeiture rate component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment for adoption of new accounting guidance		9,229
Domestic Tax Authority | Accounting standards update 2016-09, excess tax benefit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating loss carryforwards			404,700
State and Local Jurisdiction | Accounting standards update 2016-09, excess tax benefit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating loss carryforwards			6,100
Accumulated Deficit | Accounting standards update 2016-09, forfeiture rate component
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment for adoption of new accounting guidance		$ 33,349	$ 9,400	$ (9,371)