CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Restricted cash and cash equivalents	$ 73,494	$ 229,013
Short-term restricted investments (in dollars)	341,007	219,111
Other current restricted assets (in dollars)	47,949	41,121
Long term restricted investments (in dollars)	$ 20,478	$ 17,287
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	53,475	52,973
Common stock, outstanding shares	24,555	24,202
Ordinary common stock in treasury, shares	28,920	28,771