Contract Assets, Contract Liabilities and Contract Costs and Net Sales - Summary of Net Sales (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Capitalized Contract Cost [Line Items]
Net sales		$ 146,195	$ 151,843
Operating Segments [Member]
Capitalized Contract Cost [Line Items]
Net sales		146,195	151,843
Core Solutions [Member] | Operating Segments [Member]
Capitalized Contract Cost [Line Items]
Net sales	[1]	68,671	65,327
Extensions [Member] | Operating Segments [Member]
Capitalized Contract Cost [Line Items]
Net sales	[2]	$ 77,524	$ 86,516

[1] Comprehensive solutions primarily for reading, math, science and social studies programs.

[2] Primarily consists of our Heinemann brand, intervention, supplemental, and formative assessment products as well as professional services.