Pension and Other Postretirement Benefits - Schedule of Accumulated Benefit Obligation (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Qualified Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 1,024,030	$ 1,088,203
SERP
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 38,793	$ 44,343

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant