Significant Accounting Policies - Noncurrent Deferred Tax Assets Recorded in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Balance at beginning of period, Pension and Postretirement Benefit Plans	$ 79,280	$ 80,859	$ 79,938	$ 82,044
Tax effect of other comprehensive earnings, Pension and Postretirement Benefit Plans	(661)	(1,184)	(1,319)	(2,369)
Balance at end of period, Pension and Postretirement Benefit Plans	78,619	79,675	78,619	79,675
Balance at beginning of period, Unamortized Value of Terminated Forward Starting Interest Rate Swap	41	608	178	749
Tax effect of other comprehensive earnings, Unamortized Value of Terminated Forward Starting Interest Rate Swap	(41)	(144)	(178)	(285)
Balance at end of period, Unamortized Value of Terminated Forward Starting Interest Rate Swap		464		464
Balance at beginning of period, Net Noncurrent Deferred Tax Assets	79,321	81,467	80,116	82,793
Tax effect of other comprehensive earnings, Net Noncurrent Deferred Tax Assets	(702)	(1,328)	(1,497)	(2,654)
Balance at end of period, Net Noncurrent Deferred Tax Assets	$ 78,619	$ 80,139	$ 78,619	$ 80,139