Income taxes

3 Months Ended

Mar. 31, 2012

Income Tax Disclosure [Abstract]

Income taxes

Income taxes

Federal income taxes for the interim periods presented have been included in the accompanying financial statements on the basis of an estimated annual effective tax rate. The rate is based on current tax law and for 2012 does not assume reinstatement of the federal research tax credit, which expired at the end of 2011.  As of March 31, 2012, the estimated annual effective tax rate for 2012 is about 28 percent, which differs from the 35 percent statutory corporate tax rate due to the effects of non-U.S. effective tax rates.