Organization and Summary of Significant Accounting Policies (Accumulated Balances Related Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 57,182	$ 55,466
Ending balance	57,221	56,093
Unrealized Gains and (Losses) on Available for Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(523)	(574)
Other comprehensive gain (loss) before reclassifications	(476)	347
Amounts reclassified from accumulated other comprehensive loss	3
Ending balance	(996)	(227)
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(987)	(780)
Ending balance	(987)	(780)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,510)	(1,354)
Other comprehensive gain (loss) before reclassifications	(476)	347
Amounts reclassified from accumulated other comprehensive loss	3
Ending balance	$ (1,983)	$ (1,007)