Significant Accounting Policies - Noncurrent Deferred Tax Assets Recorded in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Balance at beginning of period, Pension and Postretirement Benefit Plans	$ 78,619	$ 79,675	$ 79,938	$ 82,044
Tax effect of other comprehensive earnings, Pension and Postretirement Benefit Plans	(1,326)	(1,193)	(2,645)	(3,562)
Balance at end of period, Pension and Postretirement Benefit Plans	77,293	78,482	77,293	78,482
Balance at beginning of period, Unamortized Value of Terminated Forward Starting Interest Rate Swap		464	178	749
Tax effect of other comprehensive earnings, Unamortized Value of Terminated Forward Starting Interest Rate Swap		(147)	(178)	(432)
Balance at end of period, Unamortized Value of Terminated Forward Starting Interest Rate Swap		317		317
Balance at beginning of period, Net Noncurrent Deferred Tax Assets	78,619	80,139	80,116	82,793
Tax effect of other comprehensive earnings, Net Noncurrent Deferred Tax Assets	(1,326)	(1,340)	(2,823)	(3,994)
Balance at end of period, Net Noncurrent Deferred Tax Assets	$ 77,293	$ 78,799	$ 77,293	$ 78,799