Earnings Per Share (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Weighted average shares outstanding: [Abstract]
Basic shares (in shares)	48,231,000	49,513,000	48,546,000	49,355,000
Effect of dilutive securities:
Stock options and employee stock purchase plan shares (in shares)	885,000	932,000	806,000	814,000
Diluted shares (in shares)	49,116,000	50,445,000	49,352,000	50,169,000
Anti-dilutive stock options whose exercise prices were higher than the common stock's average market price during the period (in shares)	1,384,242	1,451,858	1,419,692	1,458,858