Derivative Instruments and Hedging Activities - Derivatives Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in other comprehensive income (loss)	$ (68)	$ 79	$ (499)	$ 445
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount						$ 20,000
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	16,487		16,487		$ 18,422
Derivative assets	0		0		189
Derivative liabilities	326		326		0
Total net gain (loss)	(2)	0	29	(24)
Gain (loss) recognized in other comprehensive income (loss)			(257)		80
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	16,487		16,487		17,076
Gain (loss) recognized in other comprehensive income (loss)			(257)		80
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (loss)	(4)	1	(34)	27
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets	0		0		185
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Cash Flow Hedging [Member] | Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets	326		326
Derivative liabilities	326		326		0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	0		0		1,346
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fair Value Hedging [Member] | Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (loss)	(6)	0	(5)	0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Noninterest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total net gain (loss)	0	$ 1	0	$ 3
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative assets	0		0		4
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fair Value Hedging [Member] | Other Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities	$ 0		$ 0		$ 0