Reserves for Losses and Loss Settlement Expenses (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross liability for losses and loss settlement expenses at beginning of year	$ 1,312,483	$ 1,224,183
Ceded losses and loss settlement expenses at beginning of year	57,094	59,871
Net liability for losses and loss settlement expenses at beginning of year	1,255,389	1,164,312
Losses and loss settlement expenses incurred for claims occurring during
Current year	379,507	785,778
Prior years	4,742	(54,167)
Total incurred	384,249	731,611
Losses and loss settlement expense payments for claims occurring during
Current year	125,106	306,032
Prior years	222,102	334,502
Total paid	347,208	640,534
Net liability for losses and loss settlement expenses at end of year	1,292,430	1,255,389
Ceded losses and loss settlement expenses at end of year	49,236	57,094
Gross liability for losses and loss settlement expenses at end of period	$ 1,341,666	$ 1,312,483