Credit Agreement - Schedule of Credit Agreement (Detail) - Credit Agreement [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Credit Agreement:
Credit facility remaining availability		$ 47,782	$ 47,782
Outstanding letters of credit	[1]	2,218	2,218
Availability of additional letters of credit	[2]	$ 22,782	$ 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] As of December 31, 2018, outstanding letters of credit not related to the credit agreement totaled $0.3 million, fully collateralized with restricted cash.

[2] The letters of credit sublimit of $25.0 million as of December 31, 2019 and 2018, respectively, under the credit agreement is part of, not in addition to, the $50.0 million commitments as of December 31, 2019 and 2018, respectively.