CONSOLIDATED STATEMENTS OF INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
REVENUES
Premiums earned, affiliated	$ 640,119	$ 603,233	$ 586,609
Other income, affiliated	8,667	5,255	5,830
LOSSES AND EXPENSES
Losses and settlement expenses, affiliated	454,293	417,259	385,708
Amortization of deferred policy acquisition costs, affiliated	114,468	107,854	106,931
Other underwriting expenses, affiliated	88,930	82,044	74,370
Other expense, affiliated	$ 2,129	$ 1,825	$ 1,860