Summary of Significant Accounting Policies - Recently issued accounting pronouncements (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Jun. 30, 2015
Recent Accounting Pronouncements
Prepaid and other current assets		$ 2,967	$ 5,386
Other assets		3,797	3,020
Valuation allowance		269,882	322,721
Cumulative effect on retained earnings		(1,028,582)	(932,570)
Consolidated assets		294,676	198,864
Accumulated deficit		(1,028,582)	$ (932,570)
ASU 2015-03 | ASU Adjustment
Recent Accounting Pronouncements
Prepaid and other current assets				$ (1,000)	$ (1,200)
Other assets				$ (6,800)	$ (4,400)
ASU 2016-09 | Federal | ASU Adjustment
Recent Accounting Pronouncements
Valuation allowance		9,200
Net deferred tax assets		9,200
ASU 2016-09 | State | ASU Adjustment
Recent Accounting Pronouncements
Valuation allowance		1,200
Net deferred tax assets		$ 1,200
ASU 2014-09 | ASU Adjustment
Recent Accounting Pronouncements
Cumulative effect on retained earnings	$ 9,000
Consolidated assets	9,000
Accumulated deficit	9,000
Potential milestone payments	5,000
Minimum | ASU 2014-09 | ASU Adjustment
Recent Accounting Pronouncements
Unconstrained milestone expected reduction to accumulated deficit	4,000
Maximum | ASU 2014-09 | ASU Adjustment
Recent Accounting Pronouncements
Unconstrained milestone expected reduction to accumulated deficit	$ 6,000