Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period			$ 177,920,000
Other comprehensive income (loss)	$ 1,699	$ 9,590	2,996	$ 14,278
Balance at end of period	248,100,000		248,100,000
Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	15,882	2,394	20,473	195
Other comprehensive income (loss)	(5,260)	6,983	(9,851)	9,182
Balance at end of period	10,622	9,377	10,622	9,377
Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(171,163)	(170,533)	(175,859)	(172,384)
Other comprehensive income (loss)	5,908	1,777	10,604	3,628
Balance at end of period	(165,255)	(168,756)	(165,255)	(168,756)
Interest Rate Swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(362)	(1,173)	(390)	(445)
Other comprehensive income (loss)	(119)	32	(296)	(920)
Less reclassification adjustment for amounts included in interest expense	481	113	686	337
Balance at end of period		(1,028)		(1,028)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(75,450)	(71,082)	(76,710)	(72,712)
Other comprehensive income (loss)	738	817	1,998	2,447
Balance at end of period	(74,712)	(70,265)	(74,712)	(70,265)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(456)	(276)	(360)	(12)
Other comprehensive income (loss)	(49)	(132)	(145)	(396)
Balance at end of period	(505)	(408)	(505)	(408)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(231,549)	(240,670)	(232,846)	(245,358)
Balance at end of period	$ (229,850)	$ (231,080)	$ (229,850)	$ (231,080)