Fair Value Measurements - Assets and Liabilities at Fair Value (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Assets:
Short-term investments	$ 1,059,002,000	$ 601,217,000
Investment in Viking common stock	50,116,000	46,191,000
Investment in warrants	10,260,000	9,257,000
Total assets	1,119,378,000	656,665,000
Liabilities:
Amounts owed to former licensor	131,000	199,000
Total liabilities	13,208,000	12,741,000
Transferred over Time | Phase 3 Clinical Trial
Liabilities:
Contract asset	10,000,000
Maximum | Transferred over Time | Development, Regulatory, & Commercial Milestones and Tiered Royalties
Liabilities:
Investments	375,000,000
Crystal
Liabilities:
Contingent liabilities	4,987,000	6,477,000
CyDex
Liabilities:
Contingent liabilities	464,000	514,000
Metabasis
Liabilities:
Contingent liabilities	7,626,000	5,551,000
Level 1
Assets:
Short-term investments	5,082,000	1,326,000
Investment in Viking common stock	50,116,000	46,191,000
Investment in warrants	10,260,000	9,257,000
Total assets	65,458,000	56,774,000
Liabilities:
Amounts owed to former licensor	131,000	199,000
Total liabilities	131,000	199,000
Level 1 | Crystal
Liabilities:
Contingent liabilities	0	0
Level 1 | CyDex
Liabilities:
Contingent liabilities	0	0
Level 1 | Metabasis
Liabilities:
Contingent liabilities	0	0
Level 2
Assets:
Short-term investments	1,053,764,000	599,891,000
Investment in Viking common stock	0	0
Investment in warrants	0	0
Total assets	1,053,764,000	599,891,000
Liabilities:
Amounts owed to former licensor	0	0
Total liabilities	7,626,000	5,551,000
Level 2 | Crystal
Liabilities:
Contingent liabilities	0	0
Level 2 | CyDex
Liabilities:
Contingent liabilities	0	0
Level 2 | Metabasis
Liabilities:
Contingent liabilities	7,626,000	5,551,000
Level 3
Assets:
Short-term investments	156,000	0
Investment in Viking common stock	0	0
Investment in warrants	0	0
Total assets	156,000	0
Liabilities:
Amounts owed to former licensor	0	0
Total liabilities	5,451,000	6,991,000
Level 3 | Crystal
Liabilities:
Contingent liabilities	4,987,000	6,477,000
Level 3 | CyDex
Liabilities:
Contingent liabilities	464,000	514,000
Level 3 | Metabasis
Liabilities:
Contingent liabilities	$ 0	$ 0