Debt - Schedule of Maturity Amounts Outstanding Under Credit Agreement and Senior Unsecured Notes (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Borrowings under credit agreement, outstanding amount	$ 85,000	$ 20,000
Borrowings under note purchase and guarantee agreement, outstanding amount	449,105	449,065
Total	535,000	470,000
Unamortized debt issuance costs, net	(2,689)	(2,949)
Total debt, net	$ 532,311	$ 467,051
Revolving Facility [Member]
Line of Credit Facility [Line Items]
Maturity Date	Mar. 31, 2022	Mar. 31, 2022
Interest Rate	2.63%	2.63%
Borrowings under credit agreement, outstanding amount	$ 85,000	$ 20,000
Total	$ 85,000
Series A Notes Maturing in February 2021 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Feb. 25, 2021	Feb. 25, 2021
Interest Rate	6.00%	6.00%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 100,000	$ 100,000
Series B Notes Maturing in June 2023 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Jun. 02, 2023	Jun. 02, 2023
Interest Rate	5.35%	5.35%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 75,000	$ 75,000
Series C Notes Maturing in February 2025 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Feb. 25, 2025	Feb. 25, 2025
Interest Rate	4.75%	4.75%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 50,000	$ 50,000
Series D Notes Maturing in June 2028 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Jun. 21, 2028	Jun. 21, 2028
Interest Rate	5.47%	5.47%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 50,000	$ 50,000
Series E Notes Maturing in June 2028 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Jun. 21, 2028	Jun. 21, 2028
Interest Rate	5.47%	5.47%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 50,000	$ 50,000
Series F Notes Maturing in September 2029 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Sep. 12, 2029	Sep. 12, 2029
Interest Rate	3.52%	3.52%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 50,000	$ 50,000
Series G Notes Maturing in September 2029 [Member]
Line of Credit Facility [Line Items]
Maturity Date	Sep. 12, 2029	Sep. 12, 2029
Interest Rate	3.52%	3.52%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 50,000	$ 50,000
Series H Note Maturing In September Two Thousand Twenty Nine
Line of Credit Facility [Line Items]
Maturity Date	Sep. 12, 2029	Sep. 12, 2029
Interest Rate	3.52%	3.52%
Borrowings under note purchase and guarantee agreement, outstanding amount	$ 25,000	$ 25,000