Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Fair value, measurements, recurring
Assets:
Cash equivalents			$ 71,568	$ 4,591
Total Assets			212,483	141,184
Liabilities:
Total Liabilities			359	50,085
Fair value, measurements, recurring | Lumara Health Inc.
Liabilities:
Contingent consideration			0	49,187
Fair value, measurements, recurring | MuGard
Liabilities:
Contingent consideration			359	898
Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents			71,568	4,591
Total Assets			71,568	4,591
Liabilities:
Total Liabilities			0	0
Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Lumara Health Inc.
Liabilities:
Contingent consideration			0	0
Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | MuGard
Liabilities:
Contingent consideration			0	0
Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents			0	0
Total Assets			140,915	136,593
Liabilities:
Total Liabilities			0	0
Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2) | Lumara Health Inc.
Liabilities:
Contingent consideration			0	0
Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2) | MuGard
Liabilities:
Contingent consideration			0	0
Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents			0	0
Total Assets			0	0
Liabilities:
Total Liabilities			359	50,085
Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3) | Lumara Health Inc.
Liabilities:
Contingent consideration			0	49,187
Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3) | MuGard
Liabilities:
Contingent consideration			359	898
Corporate debt securities | Fair value, measurements, recurring
Assets:
Available-for-sale securities			113,097	116,152
Corporate debt securities | Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities			0	0
Corporate debt securities | Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities			113,097	116,152
Corporate debt securities | Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities			0	0
U.S. treasury and government agency securities | Fair value, measurements, recurring
Assets:
Available-for-sale securities			10,323	9,291
U.S. treasury and government agency securities | Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities			0	0
U.S. treasury and government agency securities | Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities			10,323	9,291
U.S. treasury and government agency securities | Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities			0	0
Commercial paper | Fair value, measurements, recurring
Assets:
Available-for-sale securities			3,995	1,999
Commercial paper | Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities			0	0
Commercial paper | Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities			3,995	1,999
Commercial paper | Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities			0	0
Certificates of deposit | Fair value, measurements, recurring
Assets:
Available-for-sale securities			13,500	9,151
Certificates of deposit | Fair value, measurements, recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities			0	0
Certificates of deposit | Fair value, measurements, recurring | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities			13,500	9,151
Certificates of deposit | Fair value, measurements, recurring | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities			0	0
Contingent Consideration
Fair value of assets and liabilities measured on a recurring basis
Adjustments to fair value of contingent consideration	$ 49,800	$ 49,900	$ (49,607)	$ (47,686)