Stock-Based Compensation - Share Based Payment Awards Granted in Period (Detail)	3 Months Ended
Mar. 31, 2018 shares
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted in period	76,404
Stock Awards (at target) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted in period	49,103
SARs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted in period	169,267

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration