Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 17,742	$ 15,315
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	114,801,901	113,741,883
Common stock, shares outstanding	82,920,231	81,860,213
Treasury stock, shares	31,881,670	31,881,670