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Amount of monthly base rent payment due in accordance with terms of a lease agreement.

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Amount of monthly lease payments including base rent and ancillary charges.

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Area of a real estate property.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

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Commitments and Contingencies (Details) $ in Thousands	1 Months Ended	3 Months Ended			9 Months Ended
Commitments and Contingencies (Details) $ in Thousands	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 13, 2018 ft²	Dec. 31, 2017 USD ($)	Mar. 31, 2016 ft²
Future minimum lease payments under non‑cancelable operating lease commitments
Recorded rent expense			$ 305	$ 101	$ 714	$ 301
Manufacturing Commitments
Minimum payments committed			34,891		34,891			$ 7,766
Wellesley Hills office
Area of leased space after expansion \| ft²									10,800
Monthly lease payments, inclusive of base rent and ancillary charges	$ 27
Lexington office
Area of leased space after expansion \| ft²							27,244
Monthly base rent payment		$ 73
Future minimum lease payments under non‑cancelable operating lease commitments
2018			218		218
2019			872		872
2020			872		872
2021			508		508
Total			$ 2,470		$ 2,470