SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details)	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) license shares	Sep. 30, 2014 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2014 USD ($) license	Mar. 20, 2014 USD ($)	Oct. 28, 1999 USD ($)
Variable Interest Entities
Net revenues		$ 497,353,000	$ 448,056,000	$ 1,463,854,000	$ 1,226,088,000
Income from equity and cost method investments		252,000	1,928,000	5,405,000	2,768,000
Decrease in accounts payable							$ 41,800,000
Pension liability		4,700,000		4,700,000			$ 4,700,000
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Adjustment to income tax provision due to credits and deductions		3,300,000
Reduction on liability for unrecognized tax benefits		5,700,000	11,000,000
Expected deferred tax benefit from sale of stock to subsidiary		$ 13,000,000		$ 13,000,000
Share Repurchase Program
Share repurchase program, authorized amount								$ 150,000,000.0	$ 150,000,000.0
Number of shares repurchased | shares		800,000.0		1,100,000
Value of shares repurchased		$ 21,000,000		$ 28,823,000	108,476,000
Total remaining authorization amount		105,500,000		$ 105,500,000
Consolidated VIEs, aggregated
Variable Interest Entities
Initial term of certain outsourcing agreements				5 years
Number of licensees as VIEs | license				37			37
Net revenues		71,000,000	68,900,000	$ 207,600,000	207,200,000
Consolidated VIEs | Eliminations
Variable Interest Entities
Liabilities associated with the certain outsourcing agreements and purchase options		76,100,000		76,100,000			$ 78,100,000
Consolidated VIEs | Eliminations | Cunningham
Variable Interest Entities
Total payments made under the LMA excluded from liabilities		36,800,000		36,800,000			34,400,000
Total capital leased liabilities excluded from VIE consolidation		4,600,000		4,600,000			4,600,000
VIEs which are not primary beneficiary
Variable Interest Entities
Carrying amount		18,900,000		18,900,000			$ 22,700,000
Income from equity and cost method investments		$ 700,000	$ 2,200,000	$ 6,500,000	$ 3,100,000
Forecast
Variable Interest Entities
Pension expense	$ 5,800,000
Actuarial losses recorded in other comprehensive income	$ 3,400,000
Maximum | Forecast
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Reduction on liability for unrecognized tax benefits						$ 1,300,000