INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Accrued expenses and other liabilities	$ 35,565	$ 25,694
Operating lease obligation	22,557
Stock-based compensation	7,657	5,167
Net operating loss and tax credit carryforwards (1)	157,202	194,773
Intangible assets, net	21,002	16,482
Investments	23,012	5,916
Unrealized foreign currency exchange losses	3,765	1,882
Other	1,017	1,021
Total deferred tax assets	271,777	250,935
Less: Valuation allowances (1)	(206,394)	(216,468)
Deferred tax assets, net of valuation allowance	65,383	34,467
Prepaid expenses and other assets	(16,343)	(12,737)
Property, equipment and software, net	(11,994)	(12,576)
Right-of-use asset	(20,172)
Convertible senior notes	(1,883)	(2,457)
Deferred revenue	(14,064)	(7,255)
Total deferred tax liabilities	64,456	35,025
Net deferred tax asset (liability)	$ 927
Net deferred tax asset (liability)		$ (558)