Workforce Reduction - General Information (Details) $ in Thousands					3 Months Ended
	Feb. 07, 2019 employee	Aug. 16, 2018 employee	Jun. 27, 2018 employee	Jan. 30, 2018 employee	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Restructuring expenses
Restructuring expenses					$ 3,328	$ 2,422
Employee severance, benefits and related costs
Restructuring expenses
Restructuring expenses					2,842
Reduction in Field-based Workforce, January 30, 2018
Workforce Reduction
Number of employees eliminated | employee				60
Restructuring expenses
Employee severance, benefits and related costs						2,400
Restructuring expenses						$ 2,400
Reduction in Headquarter-based Workforce, June 27, 2018
Workforce Reduction
Number of employees expected to be eliminated | employee			40
Reduction in Headquarter-based Workforce, June 27, 2018 | Employee severance, benefits and related costs
Restructuring expenses
Restructuring expenses					15
Reduction in Workforce, Termination of Lesinurad License Agreement, August 16, 2018
Workforce Reduction
Number of employees expected to be eliminated | employee		100
Reduction in Workforce, February 7, 2019
Workforce Reduction
Number of employees eliminated | employee	35
Number of employees expected to be eliminated | employee	35
Restructuring expenses
Employee severance, benefits and related costs					3,300
Reduction in Workforce, February 7, 2019 | Employee severance, benefits and related costs
Restructuring expenses
Restructuring expenses					$ 2,827