Debt - Expected Principal, Interest and Fee Payments on Term Loan Credit Agreement (Detail) - Term Loan Credit Agreement - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
2023, Principal	$ 41,250
2024, Principal	13,750
Total, Principal	55,000	$ 40,000
2021 (remainder), Interest and Fees	1,043
2022, Interest and Fees	4,182
2023, Interest and Fees	3,134
2024, Interest and Fees	1,826
Total, Interest and Fees	10,185
2021 (remainder), Total	1,043
2022, Total	4,182
2023, Total	44,384
2024, Total	15,576
Total	$ 65,185