Fair Value of Financial Instruments - Carrying Value and Fair Value of Long-Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 333,854	$ 362,255
Fair Value	334,279	362,663
Revolving Credit Facility Due Mar. 2020 And Nov. 2016 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	62,052	84,255
Fair Value	62,052	84,255
Term Loan, Due Feb. 2024 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	241,478	240,969
Fair Value	241,478	240,969
2.40% Term Loan, Due Jun. 2022 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	2,927	4,012
Fair Value	2,972	4,076
2.05% Term Loan, Due Mar. 2023 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	15,623	19,487
Fair Value	15,868	19,764
1.30% Term Loan, Due Jun. 2023 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	4,600	5,617
Fair Value	4,627	5,624
1.55% Term Loan, Due Sep. 2025 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	7,174	7,915
Fair Value	$ 7,282	$ 7,975