Credit Arrangements - Interest Expense, Net (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Amortization of debt discount on Convertible Notes			$ 2,570	$ 3,569
Amortization of deferred financing fees	$ 120	$ 220	485	678
Interest expense, net	1,289	2,426	5,429	7,212
Revolving Credit Facility
Debt Instrument [Line Items]
Interest / fees on Convertible Notes, Revolving Credit Facility, and other interest	185	187	636	512
Convertible Senior Notes Due 2020
Debt Instrument [Line Items]
Amortization of debt discount on Convertible Notes	594	1,201	2,570	3,569
Interest / fees on Convertible Notes, Revolving Credit Facility, and other interest	$ 390	$ 818	$ 1,738	$ 2,453