Borrowings and Credit Arrangements (Detail)			12 Months Ended
	Oct. 01, 2018 USD ($) $ / shares	Nov. 21, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	[1]	Jul. 02, 2018 USD ($)	Feb. 23, 2015 USD ($)	Oct. 24, 2014 USD ($)
Credit Facilities [Line Items]
Current portion of long-term borrowings			$ 21,423,000	$ 10,318,000
Long term borrowings			263,241,000	50,391,000
Debt offering expense			762,000	790,000	[1]	$ 0
Allocation of equity component related to the convertible senior notes, net of tax and issuance costs			12,555,000
Structured payable			302,114,000
Structured Payables
Credit Facilities [Line Items]
Current portion of long-term borrowings			1,423,000	318,000
Long term borrowings			691,000	391,000
Structured payable			2,114,000	709,000
3.50% Convertible Senior Notes due October 1, 2024 | Convertible Notes Payable
Credit Facilities [Line Items]
Debt instrument face amount	$ 150,000,000
Interest rate	3.50%
Interest expense			1,313,000
Conversion rate	0.0133
Conversion price (in dollars per share) | $ / shares	$ 75
Net proceeds from convertible notes	$ 149,000,000
Debt issuance costs	1,000,000
Debt offering expense	325,000
Liability component of debt issuance costs	1,176,000
Equity component of debt issuance costs	149,000
Unamortized debit issuance costs			$ 1,127,000
Convertible notes, liability component	133,077,000
Convertible senior notes, interest rate			5.75%
Allocation of equity component related to the convertible senior notes, net of tax and issuance costs	$ 16,923,000
Debt instrument, convertible, remaining discount amortization period	6 years
Debt discount amortization			$ 600,000
Structured payable			150,000,000
Revolving Credit Facility
Credit Facilities [Line Items]
Revolving credit facility			150,000,000	60,000,000
Current portion of long-term borrowings			20,000,000	10,000,000
Long term borrowings			130,000,000	50,000,000
Unamortized debt issuance costs			1,006,000	$ 773,000
Repayments of credit facility	$ 150,000,000
Structured payable			$ 150,000,000
Revolving Credit Facility | Credit Facility
Credit Facilities [Line Items]
Revolving credit facility										$ 50,000,000
Option to increase additional credit facility									$ 50,000,000
Line of credit interest rate during period			2.99%
Revolving Credit Facility | New Credit Agreement
Credit Facilities [Line Items]
Revolving credit facility		$ 200,000,000
Option to increase additional credit facility								$ 100,000,000
Line of credit interest rate during period			3.40%	3.00%
Line of credit , maximum borrowing capacity								$ 300,000,000
Unrestricted domestic cash and cash equivalents			$ 50,000,000
Interest coverage ratio, minimum		3.5
Interest coverage ratio, maximum		3.0
Revolving Credit Facility | New Credit Agreement | Minimum
Credit Facilities [Line Items]
Commitment fee percentage range on unused credit facility		0.15%
Revolving Credit Facility | New Credit Agreement | Maximum
Credit Facilities [Line Items]
Commitment fee percentage range on unused credit facility		0.30%
Revolving Credit Facility | New Credit Agreement | Prime Rate | Minimum
Credit Facilities [Line Items]
Basis spread on variable rate		0.00%
Revolving Credit Facility | New Credit Agreement | Prime Rate | Maximum
Credit Facilities [Line Items]
Basis spread on variable rate		0.75%
Revolving Credit Facility | New Credit Agreement | London Interbank Offered Rate (LIBOR) | Minimum
Credit Facilities [Line Items]
Basis spread on variable rate		1.00%
Revolving Credit Facility | New Credit Agreement | London Interbank Offered Rate (LIBOR) | Maximum
Credit Facilities [Line Items]
Basis spread on variable rate		1.75%

[1] Adjusted pursuant to adoption of ASU 2016-18, Statements of Cash Flows, Restricted Cash. Refer to Note 8 and Note 27 to the consolidated financial statements.