Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period			$ 335,322
Other comprehensive income (loss)	$ 1,997	$ 1,699	299	$ 2,996
Balance at end of period	292,143		292,143
Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		15,882	46,069	20,473
Change in accounting principle - ASU 2016-01			(46,069)
Balance at beginning of period, as adjusted		15,882		20,473
Other comprehensive loss - unrealized losses arising during the year		(5,260)		(9,851)
Balance at end of period		10,622		10,622
Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(167,984)	(171,163)	(164,467)	(175,859)
Other comprehensive income (loss)	1,103	5,908	(2,414)	10,604
Balance at end of period	(166,881)	(165,255)	(166,881)	(165,255)
Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period		(362)		(390)
Unrealized gains (losses) arisingduring the year		(119)		(296)
Less reclassification adjustment foramounts included in interest expense		481		686
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(70,994)	(75,450)	(72,951)	(76,710)
Other comprehensive income (loss)	959	738	2,916	1,998
Balance at end of period	(70,035)	(74,712)	(70,035)	(74,712)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(526)	(456)	(388)	(360)
Other comprehensive income (loss)	(65)	(49)	(203)	(145)
Balance at end of period	(591)	(505)	(591)	(505)
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(239,504)	(231,549)	(191,737)	(232,846)
Change in accounting principle - ASU 2016-01			(46,069)
Balance at beginning of period, as adjusted	(239,504)	(231,549)	(237,806)	(232,846)
Other comprehensive income (loss)	1,997	1,699	299	2,996
Balance at end of period	$ (237,507)	$ (229,850)	$ (237,507)	$ (229,850)