Consolidated Balance Sheets Parenthetical (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	570,000	570,000
Common stock, issued (in shares)	195,657	193,469
Common stock, outstanding (in shares)	133,854	141,172
Treasury stock, at cost (in shares)	61,803	52,297