STOCKHOLDERS' EQUITY - Effects of Share-Based Compensation on Statements of Operations (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
|
| Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] | ||||
| Share-based compensation expense | $ 77,426 | $ 58,913 | $ 217,980 | $ 157,856 |
| Cost of revenue | ||||
| Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] | ||||
| Share-based compensation expense | 38 | 18 | 88 | 79 |
| Product development | ||||
| Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] | ||||
| Share-based compensation expense | 56,321 | 39,525 | 155,114 | 103,813 |
| Sales and marketing | ||||
| Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] | ||||
| Share-based compensation expense | 6,269 | 6,108 | 20,304 | 16,703 |
| General and administrative | ||||
| Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] | ||||
| Share-based compensation expense | $ 14,798 | $ 13,262 | $ 42,474 | $ 37,261 |