Significant Accounting Policies - Recently Adopted Accounting Standards - ASU 2016-09 (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Accounting Changes
Accumulated deficit	$ (619,983,000)	$ (212,870,000)
Additional paid-in capital	1,061,325,000	1,051,953,000
Total stockholders' equity	437,775,000	840,093,000	$ 601,704,000		$ 714,615,000
Deferred tax assets before valuation allowance	140,180,000	127,338,000
Deferred tax assets valuation allowance	$ 114,955,000	$ 100,456,000
ASU 2016-09 | Early Adoption of New Accounting Principle
Accounting Changes
Accumulated deficit				$ (1,300,000)
Additional paid-in capital				1,300,000
Total stockholders' equity				0
Deferred tax assets before valuation allowance				2,400,000
Deferred tax assets valuation allowance				$ 2,400,000