Accumulated Other Comprehensive (Loss) Income - Components of Accumulated Other Comprehensive (Loss) Income, Net of Taxes (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance		$ (28,416)	$ (17,771)
Net Change		4,095	(4,666)
Ending balance		(24,238)	(26,791)
Accounting Standards Update 2017-12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]			$ 0
Accounting Standards Update 2016-01
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 0
Accounting Standards Update 2018-02
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					0
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance		(11,221)	(4,061)
Net Change		4,044	(5,015)
Ending balance		(7,177)	(10,477)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member] | Accounting Standards Update 2017-12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption	[2]			0
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member] | Accounting Standards Update 2016-01
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					(433)
Net Unrealized Holding (Losses) Gains on Available-for-Sale Investment Securities [Member] | Accounting Standards Update 2018-02
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					(968)
Net Change Related to Derivative Used for Cash Flow Hedge [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance		81	9
Net Change		(145)	183
Ending balance		19	194
Net Change Related to Derivative Used for Cash Flow Hedge [Member] | Accounting Standards Update 2017-12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption	[2]			83
Net Change Related to Derivative Used for Cash Flow Hedge [Member] | Accounting Standards Update 2016-01
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					0
Net Change Related to Derivative Used for Cash Flow Hedge [Member] | Accounting Standards Update 2018-02
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					2
Net Change Related to Defined Benefit Pension Plan [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning balance		(17,276)	(13,719)
Net Change		196	166
Ending balance		(17,080)	(16,508)
Net Change Related to Defined Benefit Pension Plan [Member] | Accounting Standards Update 2017-12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption	[2]			0
Net Change Related to Defined Benefit Pension Plan [Member] | Accounting Standards Update 2016-01
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					0
Net Change Related to Defined Benefit Pension Plan [Member] | Accounting Standards Update 2018-02
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					(2,955)
Accumulated Other Comprehensive (Loss) Income [Member]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Net Change		$ 4,095	$ (4,666)
Accumulated Other Comprehensive (Loss) Income [Member] | Accounting Standards Update 2017-12
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1],[2]			$ 83
Accumulated Other Comprehensive (Loss) Income [Member] | Accounting Standards Update 2016-01
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					(433)
Accumulated Other Comprehensive (Loss) Income [Member] | Accounting Standards Update 2018-02
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ (3,921)

[1] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2019" for additional information.

[2] (1) See Note 1, "Summary of Significant Accounting Policies - Accounting Pronouncements Adopted in 2019" for additional information.