Investment Securities - Amortized Cost and Fair Value of Available for Sale Securities Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 37,558
Available-for-sale Securities, Amortized Cost	91,984	$ 93,499
Due within twelve months, Amortized cost	18,474
Due after five but within ten years, Amortized Cost	15,367
Due after ten years, Amortized Cost	20,585
Due after one but within five years, Estimated Fair Value	15,026
Available-for-sale Securities, Estimated Fair Value	90,737	91,299
Due within twelve months, Estimated Fair Value	18,432
Due after one but within five years, Estimated Fair Value	37,011
Due after ten years, Estimated Fair Value	$ 20,268
Due after one but within five years, Book Yield	2.04%
Total securities available for sale, Book Yield	2.06%
Due within twelve months, Book Yield	1.35%
Due after five but within ten years, Book Yield	2.07%
Due after ten years, Book Yield	2.74%
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 4,952
Available-for-sale Securities, Amortized Cost	4,952	4,944
Due after one but within five years, Estimated Fair Value	4,973
Available-for-sale Securities, Estimated Fair Value	$ 4,973	4,955
Due after one but within five years, Book Yield	2.66%
Total securities available for sale, Book Yield	2.66%
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 25,091
Available-for-sale Securities, Amortized Cost	52,260	52,935
Due within twelve months, Amortized cost	17,470
Due after five but within ten years, Amortized Cost	6,255
Due after ten years, Amortized Cost	3,444
Due after one but within five years, Estimated Fair Value	6,053
Available-for-sale Securities, Estimated Fair Value	51,530	51,916
Due within twelve months, Estimated Fair Value	17,426
Due after one but within five years, Estimated Fair Value	24,612
Due after ten years, Estimated Fair Value	$ 3,439
Due after one but within five years, Book Yield	1.63%
Total securities available for sale, Book Yield	1.61%
Due within twelve months, Book Yield	1.24%
Due after five but within ten years, Book Yield	1.82%
Due after ten years, Book Yield	2.95%
Mortgage-backed Securities and CMO's [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 1,410
Available-for-sale Securities, Amortized Cost	16,419	17,217
Due after five but within ten years, Amortized Cost	7,432
Due after ten years, Amortized Cost	7,577
Due after one but within five years, Estimated Fair Value	7,302
Available-for-sale Securities, Estimated Fair Value	16,077	16,702
Due after one but within five years, Estimated Fair Value	1,405
Due after ten years, Estimated Fair Value	$ 7,370
Due after one but within five years, Book Yield	2.65%
Total securities available for sale, Book Yield	2.16%
Due after five but within ten years, Book Yield	2.04%
Due after ten years, Book Yield	2.20%
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 1,078
Available-for-sale Securities, Amortized Cost	13,326	13,373
Due within twelve months, Amortized cost	1,004
Due after five but within ten years, Amortized Cost	1,680
Due after ten years, Amortized Cost	9,564
Due after one but within five years, Estimated Fair Value	1,671
Available-for-sale Securities, Estimated Fair Value	13,205	12,955
Due within twelve months, Estimated Fair Value	1,006
Due after one but within five years, Estimated Fair Value	1,069
Due after ten years, Estimated Fair Value	$ 9,459
Due after one but within five years, Book Yield	3.23%
Total securities available for sale, Book Yield	3.12%
Due within twelve months, Book Yield	3.25%
Due after five but within ten years, Book Yield	3.13%
Due after ten years, Book Yield	3.10%
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Due after one but within five years, Amortized Cost	$ 5,027
Available-for-sale Securities, Amortized Cost	5,027	5,030
Available-for-sale Securities, Estimated Fair Value	4,952	$ 4,771
Due after one but within five years, Estimated Fair Value	$ 4,952
Due after one but within five years, Book Yield	3.05%
Total securities available for sale, Book Yield	3.05%