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Commitments and Contingencies - Additional Information (Detail)						1 Months Ended				12 Months Ended
	Jul. 01, 2019 USD ($)	Jan. 26, 2019 USD ($) ft²	May 08, 2013 ft²	Dec. 15, 2012 ft²	Dec. 06, 2011 ft²	Jun. 30, 2015 ft²	Jan. 31, 2015 ft²	Apr. 30, 2014 ft²	Jan. 31, 2014 ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 05, 2019 ft²	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 GBP (£)	Dec. 15, 2016 ft²	Nov. 01, 2013 ft²	Sep. 30, 2011 ft²	Jul. 01, 2011 ft²
Commitments And Contingencies Disclosure [Line Items]
Operating lease, rental expense \| $										$ 800,000	$ 600,000	$ 600,000
Potential payable amount over the agreement terms based on minimum purchase obligation \| $										53,000,000
Further Indication for AMR101 \| Marketing Approval In Europe
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment										9,600,000					£ 7,500,000
Further Indication for AMR101 \| Potential Marketing Approval 1
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment										6,400,000					5,000,000
Further Indication for AMR101 \| Potential Marketing Approval 2
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment										6,400,000					5,000,000
Further Indication for AMR101 \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment										$ 12,700,000					£ 10,000,000
Dublin
Commitments And Contingencies Disclosure [Line Items]
Office space leased (in square feet)																	270	320
Operating lease, expiration date										Oct. 31, 2019
Operating lease, renewal option										1 year
Operating lease, monthly rent										$ 4,900				€ 4,200
Lease termination notice period										3 months
Bedminster
Commitments And Contingencies Disclosure [Line Items]
Office space leased (in square feet)																732			9,747
Operating lease, expiration date										Apr. 30, 2019
Additional office space leased (in square feet)			10,883	2,601	2,142
Square feet vacated in exchange for reduction on future rent payments								2,000	2,142
Bedminster \| Subsequent Event
Commitments And Contingencies Disclosure [Line Items]
Operating lease, expiration date		Jun. 30, 2019
Additional office space leased (in square feet)		5,988
Monthly rent payment \| $		$ 14,000
Bedminster \| Sublease
Commitments And Contingencies Disclosure [Line Items]
Operating lease, expiration date										Sep. 30, 2017
Additional office space leased under sublease (in square feet)						2,500	4,700
Additional sublease with third party, ceased date										Mar. 31, 2018
Bridgewater \| Scenario Forecast
Commitments And Contingencies Disclosure [Line Items]
Monthly rent payment \| $	$ 141,000
Lease agreement term	11 years
Lease commencement date	Jul. 01, 2019
Bridgewater \| Subsequent Event
Commitments And Contingencies Disclosure [Line Items]
Office space lease area (in square feet)													67,747