Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) In Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' equity attributable to parent at beginning of period	$ 610,556
Other comprehensive income before reclassifications	17,740	$ 2,027
Amounts reclassified from accumulated other comprehensive loss	(6,517)	(5,857)
Net current-period other comprehensive income	11,223	(3,830)
Stockholders' equity attributable to parent at end of period	655,947	610,556
AOCI Attributable to Parent
Increase (Decrease) In Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' equity attributable to parent at beginning of period	(89,633)	(85,803)
Stockholders' equity attributable to parent at end of period	(78,410)	(89,633)
Pension and Other Postretirement Benefits Items
Increase (Decrease) In Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' equity attributable to parent at beginning of period	(84,852)	(83,279)
Other comprehensive income before reclassifications	17,740	4,284
Amounts reclassified from accumulated other comprehensive loss	(6,517)	(5,857)
Net current-period other comprehensive income	11,223	(1,573)
Stockholders' equity attributable to parent at end of period	(73,629)	(84,852)
Foreign Currency Items
Increase (Decrease) In Accumulated Other Comprehensive Income [Roll Forward]
Stockholders' equity attributable to parent at beginning of period	(4,781)	(2,524)
Other comprehensive income before reclassifications	0	(2,257)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income	0	(2,257)
Stockholders' equity attributable to parent at end of period	$ (4,781)	$ (4,781)