Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive (Loss) Income, Net of Taxes (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance		$ (17,771)	$ (19,454)	$ (16,708)
Net Change		(6,291)	1,683	(2,746)
Ending balance		(28,416)	(17,771)	(19,454)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance		(4,061)	(4,988)	(592)
Net Change		(5,759)	927	(4,396)
Ending balance		(11,221)	(4,061)	(4,988)
Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance		9	(141)	(285)
Net Change		70	150	144
Ending balance		81	9	(141)
Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Beginning balance		(13,719)	(14,325)	(15,831)
Net Change		(602)	606	1,506
Ending balance		(17,276)	(13,719)	(14,325)
Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Net Change		$ (6,291)	1,683	$ (2,746)
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			0
Accounting Standards Update 2016-01 [Member] | Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		(433)
Accounting Standards Update 2016-01 [Member] | Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		0
Accounting Standards Update 2016-01 [Member] | Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		0
Accounting Standards Update 2016-01 [Member] | Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1],[2]		(433)
Accounting Standards Update 2018-02 [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			0
Accounting Standards Update 2018-02 [Member] | Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		(968)
Accounting Standards Update 2018-02 [Member] | Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		2
Accounting Standards Update 2018-02 [Member] | Net Change Related to Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		(2,955)
Accounting Standards Update 2018-02 [Member] | Accumulated Other Comprehensive (Loss) Income [Member]
Accumulated Other Comprehensive (Loss) Income [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1],[2]		$ (3,921)

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2018" for additional information.

[2] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2018" for additional information.