Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ (87,989)	$ (84,165)	$ (89,633)	$ (85,803)
Other comprehensive income (loss) before reclassifications	3,278	1,807	6,569	4,909
Amounts reclassified from accumulated other comprehensive income	(1,646)	(1,465)	(3,293)	(2,929)
Net current-period other comprehensive income (loss)	1,632	342	3,276	1,980
Ending Balance	(86,357)	(83,823)	(86,357)	(83,823)
Pension and Other Postretirement Benefits Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(83,208)	(81,794)	(84,852)	(83,279)
Other comprehensive income (loss) before reclassifications	3,278	3,015	6,569	5,964
Amounts reclassified from accumulated other comprehensive income	(1,646)	(1,465)	(3,293)	(2,929)
Net current-period other comprehensive income (loss)	1,632	1,550	3,276	3,035
Ending Balance	(81,576)	(80,244)	(81,576)	(80,244)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(4,781)	(2,371)	(4,781)	(2,524)
Other comprehensive income (loss) before reclassifications	0	(1,208)	0	(1,055)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Net current-period other comprehensive income (loss)	0	(1,208)	0	(1,055)
Ending Balance	$ (4,781)	$ (3,579)	$ (4,781)	$ (3,579)