Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S. federal statutory income tax rate and effective tax rate
U.S. federal statutory income tax rate (as a percent)	35.00%		35.00%	35.00%	35.00%
State and local income taxes, net of U.S. federal income tax effect (as a percent)			0.60%	5.20%	0.40%
Foreign tax impact, net (as a percent)			(81.80%)	6.20%	(7.20%)
Deemed dividend on capital structure amendment (as a percent)					5.40%
Valuation allowance			585.80%
Tax impact of Tax Cuts and Jobs Act			149.20%
Stock windfall/shortfall			(13.50%)
Impact of deductible basis on the sale of energy research business ( as a percent)					(14.80%)
Reserves released upon tax settlement				18.60%
Non-deductible costs (as a percent)			21.30%	(22.80%)	6.10%
Other, net (as a percent)			7.90%	(2.10%)	(0.40%)
Effective income tax rate (as a percent)			704.50%	40.10%	24.50%
Reconciliation of the beginning and ending amounts of unrecognized tax benefits
Balance, January 1		$ 7,693	$ 7,356	$ 15,553	$ 14,395
Additions based on tax positions related to the current year			591	66	2,807
Additions based on tax positions of prior years			4	406	349
Reductions for tax positions of prior years			(13)		(36)
Reductions due to settlements with taxing authorities			(64)	(2,153)	(1,773)
Reductions due to expiration of statute of limitations			(181)	(6,516)	(189)
Balance, December 31	$ 7,693		7,693	7,356	15,553
Amount of unrecognized tax benefits that was netted against fully reserved U.S. deferred tax assets	4,500		4,500
Accrued interest expense related to tax reserves, net of related tax effects	$ 2,100		2,100
Net (reductions) additions of unrecognized tax-related interest expense			100	(2,500)	(100)
Penalties recognized, as a component of income tax expense			$ 100	$ 0	$ 0
Forecast
U.S. federal statutory income tax rate and effective tax rate
U.S. federal statutory income tax rate (as a percent)		21.00%