Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 19,576	$ 19,463
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	117,080,997	116,772,324
Common stock, shares outstanding	81,346,505	81,037,832
Treasury stock, shares	35,734,492	35,734,492