Income Taxes - Deferred (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2016
Deferred tax assets:
Net operating loss carryforwards		$ 171,437	$ 118,672
Research and development tax credit carryforwards		69,710	58,606
Property and other intangible assets		297	2,272
Deferred revenue		22,075	25,997
Stock-based compensation		12,849	12,125
Deferred lease incentive		2,639	2,889
Other liabilities		2,920	3,037
Royalty sale		38,593	47,143
Total deferred tax assets		320,520	270,741
Deferred tax liabilities:
Stock-based compensation		(156)
Royalty sale transaction costs		(625)	(859)
Total deferred tax liabilities		781	859
Valuation allowance		(319,739)	(269,882)
Net deferred tax assets/(liabilities)
Tax Cuts and Jobs Act (TCJA)
U.S. federal corporate tax rate (as a percent)	34.00%	21.00%	34.00%	34.00%
Resulting provision from revaluation of deferred tax assets and deferred tax liabilities as of TCJA enactment date		$ 97,500
Maximum
Tax Cuts and Jobs Act (TCJA)
U.S. federal corporate tax rate (as a percent)		35.00%