Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	$ 1,391	$ 955	$ 1,213
Charged to Costs and Expenses	1,239	1,469	4,174
Charged to Other Accounts	51	(270)	(373)
Deductions from Reserves	(1,708)	(763)	(4,059)
Balance at end of year	973	1,391	955
Allowance for Deferred Income Tax Assets
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	19,304	13,418	18,037
Charged to Costs and Expenses	6,700	5,706
Charged to Other Accounts	1,574	180	(2,436)
Deductions from Reserves			(2,183)
Balance at end of year	27,578	19,304	13,418
Reserve for Inventory
Valuation And Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	4,790	4,308	4,802
Charged to Costs and Expenses	3,521	876	815
Charged to Other Accounts	302	(68)	(249)
Deductions from Reserves	(726)	(326)	(1,060)
Balance at end of year	$ 7,887	$ 4,790	$ 4,308