Income Taxes - Deferred Portion of Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Accrued expenses, deducted for tax when paid	$ (21,884)	$ 15,213	$ (6,889)
Capitalized costs for books, deducted for tax	(4,832)	(5,790)	5,901
Depreciation	10,071	(4,079)	(2,405)
Tax effects of TCJA	0	34,633	0
Other, net	766	1,835	1,525
Deferred portion of the tax provision (benefit)	$ (15,879)	$ 41,812	$ (1,868)