Quantitative Information About Recurring Level 3 Fair Value Measurements (Detail) - Valuation Technique, Discounted Cash Flow [Member] - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Quantitative Information About Recurring Fair Value Measurements [Line Items]
Significant Unobservable Inputs	Probability of default	Probability of default
Range of Inputs, Minimum	2.88%	2.07%
Range of Inputs, Maximum	4.58%	3.77%
Fair Value Input Level 3
Quantitative Information About Recurring Fair Value Measurements [Line Items]
Fair Value	$ 2,568	$ 2,569