Schedule V - Valuation and Qualifying Accounts (Detail) - Allowance for doubtful accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 749	$ 711	$ 680
Charges to Earnings	528	456	470
Deductions	646	418	439
Ending Balance	$ 631	$ 749	$ 711