NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Variable Interest Entities, Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) license	Dec. 31, 2014 USD ($) license	Dec. 31, 2013 USD ($)
Variable Interest Entities
Revenue	$ 611,790	$ 548,404	$ 554,167	$ 504,775	$ 613,818	$ 494,956	$ 455,136	$ 412,648	$ 2,219,136	$ 1,976,558	$ 1,363,131
Income (loss) from equity and cost method investments									964	2,313	621
Decrease in other assets, notes payable, capital leases, and commercial bank financing					41,800					41,800
Eliminations
Variable Interest Entities
Revenue									(79,348)	(86,466)	(56,622)
Consolidated VIEs | Eliminations
Variable Interest Entities
Liabilities associated with the certain outsourcing agreements and purchase options	72,500				78,100				72,500	78,100
Consolidated VIEs | Cunningham | Eliminations
Variable Interest Entities
Total payments made under the LMA excluded from liabilities	37,600				34,400				37,600	34,400
Total capital leased assets excluded from VIE consolidation	4,500				4,300				$ 4,500	$ 4,300
Consolidated VIEs, aggregated
Variable Interest Entities
VIE licenses | license									37	37
Revenue									$ 284,400	$ 286,300	235,800
Consolidated VIEs, aggregated | Minimum
Variable Interest Entities
Variable Interest Entities Outsourcing Agreement Initial Term									5 years
VIEs which are not primary beneficiary
Variable Interest Entities
Carrying amount	$ 18,100				$ 22,700				$ 18,100	22,700
Income (loss) from equity and cost method investments									$ 7,700	$ 2,200	$ 2,100