CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,384	$ 3,246
Short-term restricted investments (in dollars)	246,968	277,556
Other current assets, restricted deposits (in dollars)	$ 32,125	$ 27,752
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	27,024	26,648
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	51,605	51,340
Common stock, outstanding shares	24,581	24,692
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