Reserves for Losses and Loss Settlement Expenses (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 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	596,771	785,778
Prior years	(770)	(54,167)
Total incurred	596,001	731,611
Losses and loss settlement expense payments for claims occurring during
Current year	229,274	306,032
Prior years	316,101	334,502
Total paid	545,375	640,534
Net liability for losses and loss settlement expenses at end of year	1,306,015	1,255,389
Ceded losses and loss settlement expenses at end of year	54,524	57,094
Gross liability for losses and loss settlement expenses at end of period	$ 1,360,539	$ 1,312,483