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Investments - Summary of Available for Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Total
Total, amortized cost	$ 10,806	$ 10,679
Total, gross unrealized gains	2,320	2,837
Total, gross unrealized losses	(63)	(53)
Total, estimated fair value	13,063	13,463
Equities
Equity securities
Equity securities, amortized cost	172	417
Equity securities, gross unrealized gains	628	1,755
Equity securities, gross unrealized losses	0	0
Equity securities, estimated fair value	800	2,172
Mutual funds
Equity securities
Equity securities, amortized cost	5,323	4,988
Equity securities, gross unrealized gains	1,432	697
Equity securities, gross unrealized losses	0	0
Equity securities, estimated fair value	6,755	5,685
U.S. Government and agency securities
Available-for-sale securities
Available-for-sale securities, amortized cost	2,317	2,039
Available-for-sale securities, gross unrealized gains	1	5
Available-for-sale securities, gross unrealized losses	(4)	0
Available-for-sale securities, estimated fair value	2,314	2,044
Corporate bonds
Available-for-sale securities
Available-for-sale securities, amortized cost	2,879	3,103
Available-for-sale securities, gross unrealized gains	259	380
Available-for-sale securities, gross unrealized losses	(6)	0
Available-for-sale securities, estimated fair value	3,132	3,483
Asset-backed securities and collateralized mortgage obligations
Available-for-sale securities
Available-for-sale securities, amortized cost	115	132
Available-for-sale securities, gross unrealized gains	0	0
Available-for-sale securities, gross unrealized losses	(53)	(53)
Available-for-sale securities, estimated fair value	$ 62	$ 79

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