Credit Agreement - Schedule of Credit Agreement (Detail) - Credit Agreement [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Credit Agreement:
Credit facility remaining availability		$ 48,582	$ 47,782
Outstanding letters of credit		1,418	2,218
Availability of additional letters of credit	[1]	$ 23,582	$ 22,782
Weighted average annual interest rate		0.00%	0.00%
Commitment fee rate		0.30%	0.30%
Letter of credit fee rate		1.25%	1.25%

[1] The letters of credit sublimit of $25.0 million under the credit agreement is part of, not in addition to, the $50.0 million borrowing limit under the credit agreement.