Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accounts receivable, allowance	$ 6,278	$ 6,448
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	289,389,000	287,123,000
Common stock, shares outstanding	289,389,000	287,123,000
Common stock in treasury, shares	102,602,000	100,781,000