Fair Value of Assets and Liabilities - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Net change in unrealized gain on investments, net of tax	$ 981	$ 147	$ 558	$ 669	$ 1,128	$ 1,081