Investments Available for Sale (Details 2)	Dec. 31, 2015	Dec. 31, 2014
Corporate debt securities
Investments available for sale
Percentage of debt securities	100.00%	100.00%
Municipal debt securities
Investments available for sale
Percentage of debt securities	100.00%	100.00%
Financial | Corporate debt securities
Investments available for sale
Percentage of debt securities	44.90%	31.30%
Consumer, non-cyclical | Corporate debt securities
Investments available for sale
Percentage of debt securities	14.80%	22.10%
Energy | Corporate debt securities
Investments available for sale
Percentage of debt securities	9.00%	9.50%
Communications | Corporate debt securities
Investments available for sale
Percentage of debt securities	7.10%	12.30%
Consumer, cyclical | Corporate debt securities
Investments available for sale
Percentage of debt securities	6.20%	5.50%
Industrial | Corporate debt securities
Investments available for sale
Percentage of debt securities	5.20%	5.50%
Utilities | Corporate debt securities
Investments available for sale
Percentage of debt securities	5.00%	3.30%
Basic materials | Corporate debt securities
Investments available for sale
Percentage of debt securities	4.00%	6.80%
Technology | Corporate debt securities
Investments available for sale
Percentage of debt securities	3.80%	3.70%
Special revenue bonds | Municipal debt securities
Investments available for sale
Percentage of debt securities	70.40%	59.70%
General obligation bonds | Municipal debt securities
Investments available for sale
Percentage of debt securities	24.50%	37.50%
Certificate of participation bonds | Municipal debt securities
Investments available for sale
Percentage of debt securities	4.00%	0.80%
Tax allocation bonds | Municipal debt securities
Investments available for sale
Percentage of debt securities	1.10%	1.50%
Special assessment bonds | Municipal debt securities
Investments available for sale
Percentage of debt securities	0.00%	0.50%