Accumulated Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period			$ 284,115
Balance at end of period	$ 301,084		301,084
Currency Translation
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(170,739)	$ (167,984)	(172,434)	$ (164,467)
Other comprehensive income (loss)	(4,500)	1,103	(2,805)	(2,414)
Balance at end of period	(175,239)	(166,881)	(175,239)	(166,881)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(73,641)	(70,994)	(75,286)	(72,951)
Other comprehensive income (loss)	818	959	2,463	2,916
Balance at end of period	(72,823)	(70,035)	(72,823)	(70,035)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(685)	(526)	(550)	(388)
Other comprehensive income (loss)	(65)	(65)	(200)	(203)
Balance at end of period	(750)	(591)	(750)	(591)
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	(245,065)	(239,504)	(248,270)	(191,737)
Change in accounting principle - ASU 2016-01				(46,069)
Balance at beginning of period, as adjusted	(245,065)	(239,504)	(248,270)	(237,806)
Other comprehensive income (loss)	(3,747)	1,997	(542)	299
Balance at end of period	$ (248,812)	$ (237,507)	$ (248,812)	$ (237,507)