Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Changes in Accumulated Other Comprehensive Income, Net of Tax by Component (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 479,517	$ 480,160	$ 549,013
Other comprehensive income (loss) before reclassifications	10,851	(283)	(2,979)
Amounts reclassified from accumulated other comprehensive income	(1,958)	(2,936)	(5,915)
Ending Balance	497,911	479,517	480,160
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	404	1,932	8,964
Other comprehensive income (loss) before reclassifications	5,020	1,515	(844)
Amounts reclassified from accumulated other comprehensive income	(2,857)	(3,043)	(6,188)
Ending Balance	2,567	404	1,932
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications	(619)
Amounts reclassified from accumulated other comprehensive income	619
Defined Benefit Plan Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,017)	(3,895)	(5,757)
Other comprehensive income (loss) before reclassifications	451	(1,229)	1,589
Amounts reclassified from accumulated other comprehensive income	280	107	273
Ending Balance	(4,286)	(5,017)	(3,895)
Foreign Currency Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(7,575)	(7,006)	(3,282)
Other comprehensive income (loss) before reclassifications	5,999	(569)	(3,724)
Ending Balance	(1,576)	(7,575)	(7,006)
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(12,188)	(8,969)	(75)
Ending Balance	$ (3,295)	$ (12,188)	$ (8,969)

Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Changes in Accumulated Other Comprehensive Income, Net of Tax by Component (Detail) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Accumulated Other Comprehensive Income (Loss) [Line Items]

Beginning Balance

$ 479,517

$ 480,160

$ 549,013

Other comprehensive income (loss) before reclassifications

10,851

(283)