Fair Values of Financial Assets and Liabilities Carried at Fair Value (Detail) - USD ($) $ in Thousands		12 Months Ended
	Sep. 29, 2017	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair values of financial liabilities, beginning balance		$ 123,200
Settlement through exchange of common shares	$ (1,900)	(1,880)
Fair values of financial liabilities, ending balance		93,500	$ 123,200
Assets Held for Sale
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair values of financial assets, beginning balance		16,700	0
Additions		0	17,300
Changes in fair value		0	(600)
Payments		(16,700)	0
Fair values of financial assets, ending balance		0	16,700
Warrant Liability
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair values of financial liabilities, beginning balance		7,400	0
Additions		0	12,800
Changes in fair value		(5,500)	(5,400)
Settlement through exchange of common shares		(1,900)
Payments		0	0
Fair values of financial liabilities, ending balance		$ 0	$ 7,400