Long-term Debt (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Long-term debt  
Long-term debt $ 50,000
Notes payable, Federal Home Loan Bank of Chicago  
Long-term debt  
Long-term debt $ 50,000
Interest rate, minimum (as a percent) 0.07%
Interest rate, maximum (as a percent) 0.13%
Weighted average rate (as a percent) 0.09%
Notes payable, Federal Home Loan Bank of Chicago | Maximum  
Long-term debt  
Notes payable maturity date 10 years