REVENUES (Impact of Changes After Adoption of Topc 606) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Liabilities
Accrued expenses and other current liabilities	$ 72,443		$ 72,443		$ 89,104	$ 89,812
Other noncurrent liabilities	16,421		16,421			9,435
Stockholders’ equity
Retained earnings	633,950		633,950		519,277	518,820
Income Statement
Revenues	445,647	$ 348,977	869,795	$ 673,628
Income from operations	54,237	40,682	102,934	71,648
Provision for/(benefit from) income taxes	6,864	5,687	(9,655)	10,641
Net income	50,255	$ 37,359	114,673	$ 61,000
Balances Without Adoption of Topic 606
Liabilities
Accrued expenses and other current liabilities	72,426		72,426			89,812
Other noncurrent liabilities	16,424		16,424
Stockholders’ equity
Retained earnings	633,964		633,964			$ 518,820
Income Statement
Revenues	444,951		869,812
Income from operations	53,541		102,951
Provision for/(benefit from) income taxes	6,728		(9,652)
Net income	49,695		114,687
Effect of Change Higher/(Lower) | Topic 606
Liabilities
Accrued expenses and other current liabilities	17		17		(708)
Other noncurrent liabilities	(3)		(3)
Stockholders’ equity
Retained earnings	(14)		(14)		$ 457
Income Statement
Revenues	696		(17)
Income from operations	696		(17)
Provision for/(benefit from) income taxes	136		(3)
Net income	$ 560		$ (14)