Net Income Per Common Share (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net Income Per Common Share [Abstract]
Average common shares outstanding during the period for basic computation	138,114,000	136,785,000	137,971,000	136,647,000
Dilutive effect of employee stock options	667,000	227,000	547,000	313,000
Average common shares outstanding during the period for diluted computation	138,781,000	137,012,000	138,518,000	136,960,000
Employee stock options excluded from calculations of diluted net income per share	933,800	2,665,445	933,800	2,665,445