Income Taxes	3 Months Ended
Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income taxes The Company uses the estimated annual effective tax rate method for calculating its tax provision in interim periods, which represents the Company's best estimate of the effective tax rate expected for the full year. The estimated annual effective tax rate typically differs from the U.S. statutory tax rate primarily as a result of tax-exempt investment income and any discrete items recognized during the period. The Company's effective tax rates were 17.9% and 17.3% for the three months ended March 31, 2019 and 2018, respectively. The decrease in the effective tax rate in the first quarter of 2019 and the first quarter of 2018 was primarily due to stock options exercised and tax-exempt interest income relative to pre-tax income.

Income Taxes

3 Months Ended

Mar. 31, 2019

Income taxes

The Company uses the estimated annual effective tax rate method for calculating its tax provision in interim periods, which represents the Company's best estimate of the effective tax rate expected for the full year. The estimated annual effective tax rate typically differs from the U.S. statutory tax rate primarily as a result of tax-exempt investment income and any discrete items recognized during the period. The Company's effective tax rates were 17.9% and 17.3% for the three months ended March 31, 2019 and 2018, respectively. The decrease in the effective tax rate in the first quarter of 2019 and the first quarter of 2018 was primarily due to stock options exercised and tax-exempt interest income relative to pre-tax income.