Derivative Financial Instruments - Details of Derivative Contracts (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Zero Cost Collar One [Member]
Derivative [Line Items]
Date of transaction	Dec. 04, 2019	Aug. 13, 2019
Type of derivative	Zero cost collar	Zero cost collar
Total notional amount	$ 15,000	$ 60,000
Month of settlement, start	2020-10	2020-01
Month of settlement, end	2020-12	2020-06
Zero Cost Collar Two [Member]
Derivative [Line Items]
Date of transaction	Jan. 31, 2020	Sep. 27, 2019
Type of derivative	Zero cost collar	Zero cost collar
Total notional amount	$ 15,000	$ 42,000
Month of settlement, start	2020-10	2020-01
Month of settlement, end	2020-12	2020-06
Zero Cost Collar Three [Member]
Derivative [Line Items]
Date of transaction	Feb. 03, 2020	Dec. 04, 2019
Type of derivative	Zero cost collar	Zero cost collar
Total notional amount	$ 9,000	$ 30,000
Month of settlement, start	2020-10	2020-07
Month of settlement, end	2020-12	2020-12
Zero Cost Collar Four [Member]
Derivative [Line Items]
Date of transaction	Feb. 21, 2020
Type of derivative	Zero cost collar
Total notional amount	$ 15,000
Month of settlement, start	2020-10
Month of settlement, end	2020-12
Zero Cost Collar Five [Member]
Derivative [Line Items]
Date of transaction	Jul. 13, 2020
Type of derivative	Zero cost collar
Total notional amount	$ 30,000
Month of settlement, start	2021-01
Month of settlement, end	2021-06