Earnings Per Share (Computation Of Basic And Diluted Net Income Per Common Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share [Abstract]
Net income (loss) attributable to OM Group, Inc. common stockholders	$ 11,949	$ 30,652
Weighted average shares outstanding - basic (in shares)	31,874	30,526
Dilutive effect of stock options and restricted stock	158	169
Weighted average shares outstanding - assuming dilution (in shares)	32,032	30,695
Earnings per common share:
Net income (loss) attributable to OM Group, Inc. common stockholders - basic (in dollars per share)	$ 0.37	$ 1.00
Net income (loss) attributable to OM Group, Inc. common stockholders - assuming dilution (in dollars per share)	$ 0.37	$ 1.00