CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Restricted cash and cash equivalents	$ 229,013	$ 81,776
Accounts receivable, allowance for doubtful accounts (in dollars)	8,622	5,644
Short-term restricted investments (in dollars)	219,111	227,795
Other current assets, restricted deposits (in dollars)	41,121	38,785
Long term restricted investments (in dollars)	$ 17,287	$ 6,306
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
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, Authorized shares	100,000	100,000
Common stock, Issued shares	52,973	51,993
Common stock, outstanding shares	24,202	23,517
Ordinary common stock in treasury, shares	28,771	28,476