Licensing Arrangements (Details) - Amended Sato Agreement												9 Months Ended
	Nov. 07, 2019 JPY (¥)	Nov. 07, 2019 USD ($)	Mar. 14, 2019 JPY (¥)	Mar. 14, 2019 USD ($)	Oct. 23, 2018 JPY (¥)	Oct. 23, 2018 USD ($)	Oct. 05, 2018 USD ($)	Jan. 19, 2017 JPY (¥)	Jan. 19, 2017 USD ($)	Jan. 12, 2017 JPY (¥)	Jan. 12, 2017 USD ($)	Sep. 30, 2019	Sep. 13, 2019 JPY (¥)	Feb. 14, 2019 JPY (¥)	Dec. 31, 2018 JPY (¥)	Dec. 31, 2018 USD ($)	Oct. 05, 2018 JPY (¥)	Jan. 12, 2017 USD ($)
Collaborative Arrangements Transactions [Line Items]
Upfront payment receivable																	¥ 1,250,000,000
Upfront payment installments													¥ 500,000,000	¥ 500,000,000			250,000,000
Payment received under license agreement			¥ 500,000,000	$ 4,460,000	¥ 250,000,000	$ 2,224,000		¥ 1,250,000,000	$ 10,813,000	¥ 1,250,000,000	$ 10,813,000
Aggregate development and regulatory milestone payments potentially receivable under license agreement										2,750,000,000							1,750,000,000
Aggregate Phase 1 trial milestone payment term under license agreement										250,000,000					¥ 250,000,000	$ 2,162,000		$ 2,162,000
Aggregate becoming payable upon earlier of specified future dates or achievement of milestone events																	1,000,000,000
Aggregate commercial milestone payments potentially receivable under license agreement										¥ 900,000,000							¥ 3,900,000,000
License agreement additional term												2 years
Maximum preclinical studies amount | $											$ 1,000,000
Written notice to terminate, period										120 days	120 days
Written notice to terminate due to material breach, term										60 days	60 days
Upfront fee refundable in event of termination | $							$ 0
Subsequent Event
Collaborative Arrangements Transactions [Line Items]
Payment received under license agreement	¥ 500,000,000.0	$ 4,554,000