Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts	$ 27,387	$ 24,510
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	120,000,000	120,000,000
Common Stock, shares issued	73,129,194	72,740,302
Common Stock, shares outstanding	73,129,194	72,740,302
Preferred Stock, par value	$ 0.01	$ 0.01
Preferred Stock, shares authorized	1,000,000	1,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Treasury Stock at cost, shares	246,037	246,037