FAIR VALUE MEASUREMENT - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value Measured on a Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Level III
Liabilities:
Contingent consideration related to 2017 and 2018 acquisitions	$ 6,733	$ 32,233
Prepaid forward contracts | Level II
Assets:
Derivative asset	31,510	52,545
Liabilities:
Derivative liability	10,131	162,049
Interest rate swap contracts | Level II
Assets:
Derivative asset	3,269	0
Liabilities:
Derivative liability	143,719	77,902
Investment securities pledged as collateral | Level I
Assets:
Investment securities	1,521,045	1,720,357
Money market funds | Level I
Assets:
Cash and cash equivalents	$ 296,123	$ 5,949