Income Taxes - Expense (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of the expected statutory tax benefit to the actual income taxes
U.S. federal corporate tax rate (as a percent)		34.00%
Loss before income tax expense	$ (78,883)	$ (96,012)	$ (144,817)	$ (60,739)
Expected tax benefit at 34%	(26,820)	(32,644)	(49,238)	(20,651)
Permanent differences	15	25	345	818
Incentive stock options	1,313	1,528	2,501	1,948
State tax benefit net of federal benefit	(4,157)	(3,537)	(7,954)	(3,252)
Change in valuation allowance, net	32,922	(63,238)	62,505	27,940
Federal research credit	(1,232)	(2,204)	(4,109)	(1,407)
Federal orphan drug credit	(2,901)	(7,118)	(4,241)	(5,471)
Expired loss and credit carryforwards			184	$ 75
Change in U.S. tax law		97,479
Debt inducement		8,044
Stock option expirations	$ 860	$ 1,665	$ 7