Concentrations of Credit Risk (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Concentrations of Credit Risk [Abstract]
Guarantor obligations, aggregate amount of collateral held	$ 333,188
Collateral held that is equal to the ultimate losses that would be paid or due in the event of insured's default	100.00%
Uncollateralized exposure as a percentage of shareholder's equity	70.00%
Largest estimated amounts due from individual reinsurers	$ 48,473