CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 4,612	$ 3,336
Short-term restricted investments (in dollars)	88,332	129,599
Other current assets, restricted deposits (in dollars)	$ 20,846	$ 20,453
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, Authorized shares	10,000	10,000
Preferred stock, Issued shares	0	0
Preferred stock, outstanding shares	0	0
Ordinary common stock in treasury, shares	18,575	18,112
Ordinary common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, Authorized shares	100,000	100,000
Common stock, Issued shares	45,928	45,285
Common stock, outstanding shares	27,353	27,173
Multi-Vote common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, Authorized shares	40,000	40,000
Common stock, Issued shares	0	0
Common stock, outstanding shares	0	0