Debt - Schedule of Maturity Amounts Outstanding Under Credit Agreement and Second Restated Prudential Note Purchase Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Borrowings under purchase agreement, outstanding amount	$ 224,627	$ 174,743
Borrowings under credit agreement, outstanding amount	73,976	123,801
Total	300,000	300,000
Unamortized debt issuance costs, net	(1,397)	(1,456)
Total debt, net	$ 298,603	$ 298,544
Revolving Facility [Member]
Line of Credit Facility [Line Items]
Maturity Date	Jun. 02, 2018	Jun. 02, 2018
Interest Rate	3.33%	3.33%
Borrowings under credit agreement, outstanding amount	$ 25,000	$ 75,000
Total	$ 25,000
Term Loan [Member]
Line of Credit Facility [Line Items]
Maturity Date	Jun. 02, 2020	Jun. 02, 2020
Interest Rate	3.28%	3.28%
Borrowings under credit agreement, outstanding amount	$ 50,000	$ 50,000
Total	$ 50,000
Series A Notes Maturing on 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 purchase agreement, outstanding amount	$ 100,000	$ 100,000
Series B Notes Maturing on 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 purchase agreement, outstanding amount	$ 75,000	$ 75,000
Series C Notes Maturing on 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 purchase agreement, outstanding amount	$ 50,000