Derivative Financial Instruments - Effect of Derivative Instruments on Consolidated Statement of Earnings (Detail) - Derivatives Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Amount of Gain Recognized in Income on Derivative Instruments	$ 73	$ 198	$ 340	$ 592
Interest Rate Swaps [Member] \| Other Income [Member]
Derivatives, Fair Value [Line Items]
Amount of Gain Recognized in Income on Derivative Instruments	$ 73	$ 198	$ 340	$ 592

Amount of increase in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

Name:	us-gaap_DerivativeGainOnDerivative
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration