STATEMENT OF ACCOUNTING POLICIES, RESTRICTED CASH AND STOCK-BASED COMPENSATION (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended					1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2012 Performance Shares [Member]	May 31, 2012 Non-Employee Directors [Member] Restricted Stock [Member]	Dec. 31, 2012 Non-Employee Directors [Member] Restricted Stock [Member]	Mar. 31, 2012 President and Chief Executive Officer [Member] Restricted Stock [Member]	Dec. 31, 2012 President and Chief Executive Officer [Member] Restricted Stock [Member]	Mar. 31, 2012 Management [Member] Performance Shares [Member]	Dec. 31, 2012 Management [Member] Performance Shares [Member]
Restricted cash [Abstract]
Restricted cash	$ 2,800	$ 6,500
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)									5 years		3 years
Number of shares granted (in shares)				25,747	122,302		23,461		2,286		119,640
Weighted average grant date fair value (in dollars per share)				$ 35.51	$ 34.2	$ 33.42		$ 34.45		$ 34.45
Vesting rights									equal annual installments over a five year period
Total stock-based compensation expense	$ 4,900	$ 5,300	$ 4,100