Balance Sheet Parenthetical (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Restricted investments	430	430
Allowances for accounts receivable	35	35
Accumulated depreciation and amortization, property and equipment	80,882	83,416
Preferred stock, par value per share	0.01	0.01
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	0.001	0.001
Common stock, shares authorized	900,000	900,000
Treasury stock, shares	814	380
Common Stock [Member]
Common stock, shares issued	513,835	512,375