Losses and Loss Adjustment Reserve - Effects of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Written
Direct premiums	$ 619,223	$ 604,623
Assumed premiums	0	0
Ceded premiums	619,206	604,610
Net premiums	17	13
Earned
Direct premiums	602,320	592,267
Assumed premiums	0	0
Ceded premiums	602,303	592,254
Net premiums	$ 17	$ 13