Consolidated Balance Sheets Parenthetical (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
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)	197,196	197,080
Common stock, outstanding (in shares)	134,688	134,573
Treasury stock, at cost (in shares)	62,508	62,507