Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Tax Effects Related to the Change in Each Component of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Unrealized gains (losses) on available-for-sale securities, Before-Tax Amount	$ 8,230	$ 2,484	$ (1,384)
Unrealized gains (losses) on available-for-sale securities, Tax (Expense) Benefit	(3,210)	(969)	540
Unrealized gains (losses) on available-for-sale securities, Net-of-Tax Amount	5,020	1,515	(844)
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Before-Tax Amount	(4,684)	(4,989)	(10,145)
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Tax (Expense) Benefit	1,827	1,946	3,957
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Net-of-Tax Amount	(2,857)	(3,043)	(6,188)
Unrealized gains (losses) on cash flow hedges, Before-Tax Amount	(897)
Unrealized gains (losses) on cash flow hedges, Tax (Expense) Benefit	278
Unrealized gains (losses) on cash flow hedges, Net-of-Tax Amount	(619)
Reclassification adjustment for amounts related to cash flow hedges included in net income, Before-Tax Amount	897
Reclassification adjustment for amounts related to cash flow hedges included in net income, Tax (Expense) Benefit	(278)
Reclassification adjustment for amounts related to cash flow hedges included in net income, Net-of-Tax Amount	619
Defined benefit plan adjustments, Before-Tax Amount	654	(1,782)	2,303
Defined benefit plan adjustments, Tax (Expense) Benefit	(203)	553	(714)
Defined benefit plan adjustments, Net-of-Tax Amount	451	(1,229)	1,589
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Before-Tax Amount	406	156	396
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Tax (Expense) Benefit	(126)	(49)	(123)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Net-of-Tax Amount	280	107	273
Foreign currency translation adjustment, Before-Tax Amount	5,999	(569)	(3,724)
Foreign currency translation adjustment, Net-of-Tax Amount	5,999	(569)	(3,724)
Total Other Comprehensive Income (Loss), Before-Tax Amount	10,605	(4,700)	(12,554)
Total Other Comprehensive Income (Loss), Tax (Expense) Benefit	(1,712)	1,481	3,660
Other Comprehensive Income (Loss), net of tax	$ 8,893	$ (3,219)	$ (8,894)