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Revenue Recognition - Additional Information (Detail) ¥ in Billions		1 Months Ended		3 Months Ended		10 Months Ended
	May 17, 2018 USD ($) PerformanceObligation	Apr. 30, 2013 USD ($) PerformanceObligation	Apr. 30, 2012 USD ($)	Mar. 31, 2019 USD ($) PerformanceObligation Milestone	Mar. 31, 2018 Milestone	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2013 JPY (¥)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue, current				$ 28,194,000		$ 28,194,000	$ 26,825,000
Deferred revenue, non current				9,573,000		9,573,000	15,184,000
Total revenue				$ 4,382,000
Number of remaining performance obligations \| PerformanceObligation				0
Number of milestone event probable of occurrence or achieved \| Milestone				0	0
License and Milestone Fees [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue				$ 4,242,000
Royalty [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue from contract with customer				0
VFMCRP Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue, current				28,194,000		28,194,000	26,825,000
Deferred revenue, non current				9,573,000		9,573,000	15,184,000
Receivables				0		0	0
Other assets				0		0	0
Deferred revenue	$ 55,444,000						0
Number of combined performance obligations for revenue recognized \| PerformanceObligation	1
Number of performance obligations for revenue recognized \| PerformanceObligation	2
upfront payment	$ 50,000,000
Premium from sale of stock	$ 5,444,000
Remaining performance obligations				$ 37,767,000		$ 37,767,000
Remaining performance obligation, expected timing of satisfaction, year				2020		2020
VFMCRP Agreement [Member] \| License and Milestone Fees [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue				$ 4,242,000		$ 17,677,000
Maruishi and CKDP Agreements [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Receivables				0		0	0
Other assets				0		0	0
Deferred revenue				$ 0		$ 0	$ 0
Maruishi Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Number of performance obligations for revenue recognized \| PerformanceObligation		2		2
Premium from sale of stock		$ 337,000
Upfront non-refundable, non-creditable license fee and premium from sale of stock		15,337,000
Maruishi Agreement [Member] \| Clinical Development and Regulatory Milestones [Member] \| Maximum [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration		10,500,000
Maruishi Agreement [Member] \| One-time Sales Milestone [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration \| ¥								¥ 1
Maruishi Agreement [Member] \| License [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Estimated selling price		10,200,000
Upfront payments on obligations		9,637,000
Maruishi Agreement [Member] \| R&D Services [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Estimated selling price		6,200,000
Upfront payments on obligations		$ 5,700,000
CKDP Agreement [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Premium from sale of stock			$ 83,000
CKDP Agreement [Member] \| Clinical Development and Regulatory Milestones [Member] \| Maximum [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Remaining potential consideration			3,750,000
CKDP Agreement [Member] \| License [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Revenue from contract with customer			$ 646,000