Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period			$ 284,115
Balance at end of period	$ 306,671		306,671
Currency Translation
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(172,459)	$ (161,876)	(172,434)	$ (164,467)
Other comprehensive income (loss)	1,720	(6,108)	1,695	(3,517)
Balance at end of period	(170,739)	(167,984)	(170,739)	(167,984)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(74,458)	(71,968)	(75,286)	(72,951)
Other comprehensive income (loss)	817	974	1,645	1,957
Balance at end of period	(73,641)	(70,994)	(73,641)	(70,994)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(620)	(461)	(550)	(388)
Other comprehensive income (loss)	(65)	(65)	(135)	(138)
Balance at end of period	(685)	(526)	(685)	(526)
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period				46,069
Change in accounting principle – ASU 2016-01				(46,069)
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(247,537)	(234,305)	(248,270)	(191,737)
Change in accounting principle – ASU 2016-01				(46,069)
Balance at beginning of period, as adjusted	(247,537)	(234,305)	(248,270)	(237,806)
Other comprehensive income (loss)	2,472	(5,199)	3,205	(1,698)
Balance at end of period	$ (245,065)	$ (239,504)	$ (245,065)	$ (239,504)