Financial Instruments - Valuation Approach Applied to Each Class of Security (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash	$ 3,041			$ 6,681
Adjusted Cost	3,133			16,258
Unrealized Gains	0			0
Unrealized Losses	0			(304)
Fair Value	3,133			15,954
Cash and Cash Equivalents	3,133			12,773
Long-Term Notes Receivables and Other Assets, net	0			3,181
Unrealized gain (loss) during period	2,300	$ 400	$ 700
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjusted Cost				9,577
Unrealized Gains				0
Unrealized Losses				(304)
Fair Value				9,273
Cash and Cash Equivalents				6,092
Long-Term Notes Receivables and Other Assets, net				3,181
Money market funds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjusted Cost	92			6,092
Unrealized Gains	0			0
Unrealized Losses	0			0
Fair Value	92			6,092
Cash and Cash Equivalents	92			6,092
Long-Term Notes Receivables and Other Assets, net	$ 0			0
Corporate securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjusted Cost				3,485
Unrealized Gains				0
Unrealized Losses				(304)
Fair Value				3,181
Cash and Cash Equivalents				0
Long-Term Notes Receivables and Other Assets, net				$ 3,181