Commitments and Contingencies - Additional Information (Detail) $ in Millions			1 Months Ended						9 Months Ended
	Oct. 01, 2018 ft²	Dec. 31, 2017 ft²	Jul. 31, 2018 ft²	Feb. 28, 2017 ft²	Oct. 31, 2016	Sep. 30, 2016	May 31, 2016	Sep. 30, 2015 Patent	Dec. 31, 2018 USD ($)	Mar. 31, 2018 ft²
Magnetic Clutch Patents
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent								2
European Pigtail Patent
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent								1
German Pigtail Patent
Commitments and Contingencies [Line Items]
Patents allegedly infringed upon, number | Patent								1
Patent One
Commitments and Contingencies [Line Items]
Patent expiration period							2020-09
Patent Two
Commitments and Contingencies [Line Items]
Patent expiration period							2020-12
Patent Three
Commitments and Contingencies [Line Items]
Patent expiration period							2021-10
Lease Agreements | Massachusetts
Commitments and Contingencies [Line Items]
Annual rent expense | $									$ 0.9
Lease expiration date		Aug. 31, 2025	Sep. 30, 2027	Jul. 31, 2022
Additional office space | ft²		6,607	23,864	21,603						11,269
Total office space | ft²	63,343
Lease Agreements | Germany
Commitments and Contingencies [Line Items]
Annual rent expense | $									0.3
Lease commencement period						2017-05
Lease expiration period						2024-05
Lease Agreements | Japan
Commitments and Contingencies [Line Items]
Annual rent expense | $									$ 0.9
Lease expiration period					2021-09