Stock-Based Compensation - Share Based Payment Awards Granted in Period (Detail)	6 Months Ended
Jun. 30, 2018 shares
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted in period	76,409
Stock Awards (at target) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted in period	48,911
SARs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards granted in period	169,245

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