Significant Accounting Policies (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Number of operating segments | Segment	1
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings	$ (435,890)	$ (424,907)	$ (409,478)	$ (426,385)		$ (386,735)	$ (331,428)	$ (325,838)	$ (301,818)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings		$ 609
Retained Earnings (Accumulated Deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings	$ 32,783	(14,235)	$ 37,140	$ 1,847		$ 16,453	$ 10,213	$ 6,994	$ 12,908
Retained Earnings (Accumulated Deficit) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings		$ 609			$ 600