Schedule II - Condensed Financial Information of the Registrant Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statements of Income and Comprehensive Income
Revenues	$ 223,899	$ 215,273	$ 216,002	$ 222,579	$ 202,901	$ 215,907	$ 207,970	$ 209,719	$ 877,753	$ 836,497	$ 839,113
Expenses									754,072	732,246	752,413
Net income	$ 28,102	$ 15,619	$ 25,934	$ 29,946	$ 18,346	$ 28,908	$ 26,816	$ 9,125	99,601	83,195	62,387
Other comprehensive (loss) income, net of tax									38,896	(22,816)	8,426
Comprehensive income									138,497	60,379	70,813
Registrant
Condensed Statements of Income and Comprehensive Income
Expenses									1,694	1,695	1,494
Net loss									(1,694)	(1,695)	(1,494)
Earnings from consolidated subsidiaries									101,295	84,890	63,881
Net income									99,601	83,195	62,387
Other comprehensive (loss) income, net of tax									38,896	(22,816)	8,426
Comprehensive income									$ 138,497	$ 60,379	$ 70,813