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Equity Plans (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
Equity Plans (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deemed repurchases of restricted stock units					$ 8,947	$ 23,019
Share-based compensation expense			$ 12,394	$ 13,841	$ 43,141	$ 50,465
Total unrecognized share-based compensation costs, remaining period of recognition					1 year 8 months 12 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares surrendered to the Company for tax withholding					199,377
Total unrecognized share-based compensation costs			$ 47,400		$ 47,400
RSUs \| Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested in period					477,764
New shares of Company's Class A common stock issued					278,387
PRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares surrendered to the Company for tax withholding					142,882
PRSUs \| Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested in period					325,836
New shares of Company's Class A common stock issued					182,954
2016 Employee Stock Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period (in units)		1,171,956
Vesting period (in years)					3 years
2011 Stock Plan for Non-Employee Directors \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period (in units)	54,535
Share-based Compensation Award, Tranche One \| 2016 Employee Stock Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period (in units)		380,142