Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 15,315	$ 14,256
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	113,741,883	111,522,354
Common stock, shares outstanding	81,860,213	79,655,213
Treasury stock, shares	31,881,670	31,867,141