Reinsurance - Effect of Reinsurance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Insurance [Abstract]
Direct premiums	$ 2,464,870	$ 2,499,584	$ 2,341,088
Reinsurance premiums assumed from other companies	236,504	286,165	227,053
Reinsurance premiums ceded to other companies	(518,580)	(557,556)	(500,939)
Net premiums	$ 2,182,794	$ 2,228,193	$ 2,067,202