Income Taxes - Deferred Portion of Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Accrued expenses, deducted for tax when paid	$ (19,115)	$ (17,797)	$ (21,884)
Capitalized costs for books, deducted for tax	1,904	3,246	(4,832)
Depreciation	6,732	3,526	10,071
Other, net	(1,260)	2,153	766
Deferred portion of the tax provision (benefit)	$ (11,739)	$ (8,872)	$ (15,879)