Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) FinancialInstitution	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) FinancialInstitution	Jan. 01, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 746	$ 868	$ 746	$ 868	$ 1,854
Content licensing expenses			4,100		1,700
Amortization of content license assets	4,900	$ 600	17,131	$ 1,344
Cumulative-effect adjustment to accumulated deficit	$ 399,712		$ 399,712		$ 313,833
Accounting Standards Update 2016-13
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020		Jan. 01, 2020
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment | Revision of Prior Period, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Cumulative-effect adjustment to accumulated deficit						$ 1,100
Accounting Standards Update 2019-02
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true		true
Accounting Standards Update 2018-15
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true		true
Accounting Standards Update 2018-13
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true		true
Accounting Standards Update 2017-04
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true		true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2020		Jan. 01, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true		true
Customer 1
Summary Of Significant Accounting Policies [Line Items]
Number of financial institutions which manage cash balances | FinancialInstitution			1		1
Customer 1 | Cash and Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Percentage of cash and cash equivalents balances			48.00%		65.00%
Customer 2
Summary Of Significant Accounting Policies [Line Items]
Number of financial institutions which manage cash balances | FinancialInstitution			1		1
Customer 2 | Cash and Cash Equivalents
Summary Of Significant Accounting Policies [Line Items]
Percentage of cash and cash equivalents balances			23.00%		34.00%