DEBT - COVERTIBLE SUBORDINATED NOTES (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Payments On Zero Coupon Subordinated Notes	$ 18,900,000	$ 21,500,000	$ 8,200,000
Common stock issued upon conversion of zero-coupon subordinated notes (in shares)	0.1	0.1	0
Zero-coupon convertible subordinated notes [Member]
Debt Instrument [Line Items]
Principal amount at maturity of zero-coupon subordinated notes outstanding	106,900,000		128,800,000
Issued price per principal amount at maturity	671.65
Principal amount of zero-coupon subordinated notes	1,000.0
Annual yield to maturity	2.00%
Stock conversion rate for zero-coupon subordinated notes (per thousand)	13.4108
Minimum number of trading days in a period the common stock sale price must meet a specified threshold to trigger conversion price (in days)	20
Number of consecutive trading days ending on the last trading day of the preceding quarter for the common stock sale price to reach a specified threshold to trigger conversion price (in days)	30
Common stock sales price threshold, beginning	120.00%
Common stock sales price threshold, declining per quarter	0.1282%
Common stock sales price threshold, ending	110.00%
Conversion trigger price, current period (per share)	$ 73.97
Principal Amount At Maturity Of Zero Coupon Subordinated Notes Converted	21,900,000	25,500,000
Value Of Cash And Common Stock In Connection With Conversions Of Zero Coupon Subordinated Notes Settled In Current Period	28,700,000	31,800,000
Payments On Zero Coupon Subordinated Notes	18,900,000	21,500,000
Common stock issued upon conversion of zero-coupon subordinated notes (in shares)	0.1	0.1
Tax Benefit Realized Upon Conversion Of Zero Coupon Convertible Debt	$ 3,800,000	$ 3,400,000
Contingent cash interest accrual rate period	September 12, 2014 to March 11, 2015
Contingent cash interest accrual rate description	no less than 0.125% of the average market price of a zero-coupon subordinated note for the five trading days ended September 9, 2014, in addition to the continued accrual of the original issue discount
Contingent cash interest accrual rate	0.125%
Number of days used to establish average market price of zero coupon subordinated notes	5
Debt Conversion Announcement Date	Jan. 02, 2015
Debt Conversion Date Of Subordinated Notes And Indenture	Oct. 24, 2006
Zero Coupon Subordinated Notes Convertible Earliest Date	Jan. 01, 2015
Zero Coupon Subordinated Notes Convertible Latest Date	Mar. 31, 2015