Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock-based compensation expense, by operating expense category
Stock-based compensation expense	$ 22,965	$ 15,869
Platform operations
Stock-based compensation expense, by operating expense category
Stock-based compensation expense	1,462	1,056
Sales and marketing
Stock-based compensation expense, by operating expense category
Stock-based compensation expense	5,314	3,227
Technology and development
Stock-based compensation expense, by operating expense category
Stock-based compensation expense	8,590	4,936
General and administrative
Stock-based compensation expense, by operating expense category
Stock-based compensation expense	$ 7,599	$ 6,650