SEGMENT REPORTING - Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Revenue and long-lived assets excluding intangible assets, by geographical area
Revenue	$ 146,531	$ 119,028
Long-lived assets	89,275		$ 93,686
United States
Revenue and long-lived assets excluding intangible assets, by geographical area
Revenue	123,084	101,668
Long-lived assets	80,049		84,137
United Kingdom
Revenue and long-lived assets excluding intangible assets, by geographical area
Revenue	13,650	13,690
Other countries
Revenue and long-lived assets excluding intangible assets, by geographical area
Revenue	9,797	$ 3,670
Long-lived assets	$ 9,226		$ 9,549