Allowance for Loan and Lease Losses - Allowance for Credit Losses - Reserves (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Specific	$ 2,059		$ 2,008
General	9,141		7,742
Ending balance	11,200	$ 9,883	9,750	$ 9,043
Unallocated [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
General	(2)		30
Ending balance	(2)	12	30	46
Real Estate Sector [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific	1,691		937
General	5,033		4,894
Ending balance	6,724	5,969	5,831	4,786
Agricultural Sector [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific	1		2
General	190		254
Ending balance	191	201	256	208
Commercial and Industrial and Mortgage Warehouse Sector [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific	133		918
General	2,728		1,476
Ending balance	2,861	2,569	2,394	2,772
Consumer Loans Sector [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific	234		151
General	1,192		1,088
Ending balance	$ 1,426	$ 1,132	$ 1,239	$ 1,231