CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 5,197	$ 5,447
Short-term restricted investments (in dollars)	138,929	117,674
Other current assets, restricted deposits (in dollars)	$ 29,340	$ 25,009
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	20,872	19,735
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	49,688	47,351
Common stock, outstanding shares	28,816	27,616
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