Revolving Credit Facility (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Actual net worth for compliance	$ 175,700,000
Minimum net worth required for compliance	95,000,000
Ratio of total liability to net worth	0.3
Maximum ratio of total liability to net worth for compliance	2
Actual working capital for compliance	88,400,000
Minimum working capital for compliance	40,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum borrowings	30,000,000.0
Standby letter of credit	800,000
Borrowings available under the revolving credit facility	29,200,000
Frequency of periodic payments	monthly
Fees associated with unused portion of committed amount	0
Borrowings outstanding under revolving credit facility	$ 0	$ 0
Weighted average interest rate	2.70%	2.70%
Revolving Credit Facility [Member] | LIBOR [Member]
Line of Credit Facility [Line Items]
Stated percentage	2.50%