Reserves for Insurance Claims and Claim Expenses - Reconciliation of Reserve Balances for Insurance Claims Expense (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Beginning balance $ 8,761 $ 3,001
Less reinsurance recoverables 1,902 297
Beginning balance, net of reinsurance recoverables 6,859 2,704
Claims incurred:    
Current year 3,152 2,331
Prior years (940) (323)
Total claims and claims expenses incurred 2,212 2,008
Claims and claim expenses paid:    
Current year 0 0
Prior years 852 563
Total claims and claim expenses paid 852 563
Ending balance, net of reinsurance recoverables 8,219 4,149
Add reinsurance recoverables 2,382 899
Ending balance $ 10,601 $ 5,048