Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair value, measurements, recurring - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 120,778	$ 4,591
Total assets	261,146	141,184
Liabilities:
Total liabilities	823	50,085
Lumara Health Inc.
Liabilities:
Contingent consideration		49,187
MuGard
Liabilities:
Contingent consideration	823	898
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	120,778	4,591
Total assets	120,778	4,591
Liabilities:
Total liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Lumara Health Inc.
Liabilities:
Contingent consideration		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | MuGard
Liabilities:
Contingent consideration	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Total assets	140,368	136,593
Liabilities:
Total liabilities	0	0
Significant Other Observable Inputs (Level 2) | Lumara Health Inc.
Liabilities:
Contingent consideration		0
Significant Other Observable Inputs (Level 2) | MuGard
Liabilities:
Contingent consideration	0	0
Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Total assets	0	0
Liabilities:
Total liabilities	823	50,085
Significant Unobservable Inputs (Level 3) | Lumara Health Inc.
Liabilities:
Contingent consideration		49,187
Significant Unobservable Inputs (Level 3) | MuGard
Liabilities:
Contingent consideration	823	898
Corporate debt securities
Assets:
Available-for-sale securities	108,128	116,152
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
Corporate debt securities | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	108,128	116,152
Corporate debt securities | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	0	0
U.S. treasury and government agency securities
Assets:
Available-for-sale securities	12,278	9,291
U.S. treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
U.S. treasury and government agency securities | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	12,278	9,291
U.S. treasury and government agency securities | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	0	0
Certificates of deposit
Assets:
Available-for-sale securities	14,500	9,151
Certificates of deposit | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
Certificates of deposit | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	14,500	9,151
Certificates of deposit | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	0	0
Commercial paper
Assets:
Available-for-sale securities	5,462	1,999
Commercial paper | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Available-for-sale securities	0	0
Commercial paper | Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale securities	5,462	1,999
Commercial paper | Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale securities	$ 0	$ 0