Loans and Allowance for Loan Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) loan	Mar. 31, 2018 loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	0	2
Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	31		33
Troubled debt, balance | $	$ 8,800		$ 9,215
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	12		12
Troubled debt, balance | $	$ 6,297		$ 6,369
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	19		21
Troubled debt, balance | $	$ 2,503		$ 2,846
Real estate
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts		1
Real estate | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	22		23
Troubled debt, balance | $	$ 5,553		$ 5,664
Real estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	8		8
Troubled debt, balance | $	$ 3,477		$ 3,536
Real estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	14		15
Troubled debt, balance | $	$ 2,076		$ 2,128
Real estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3		3
Troubled debt, balance | $	$ 480		$ 485
Real estate | Construction | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	0		0
Troubled debt, balance | $	$ 0		$ 0
Real estate | Construction | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3		3
Troubled debt, balance | $	$ 480		$ 485
Real estate | Single family residential
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts		1
Real estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	15		16
Troubled debt, balance | $	$ 820		$ 846
Real estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	6		6
Troubled debt, balance | $	$ 227		$ 230
Real estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	9		10
Troubled debt, balance | $	$ 593		$ 616
Real estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	4		4
Troubled debt, balance | $	$ 4,253		$ 4,333
Real estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		2
Troubled debt, balance | $	$ 3,250		$ 3,306
Real estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		2
Troubled debt, balance | $	$ 1,003		$ 1,027
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	9		10
Troubled debt, balance | $	$ 3,247		$ 3,551
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	4		4
Troubled debt, balance | $	$ 2,820		$ 2,833
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	5		6
Troubled debt, balance | $	$ 427		$ 718
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	9		10
Troubled debt, balance | $	$ 3,247		$ 3,551
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	4		4
Troubled debt, balance | $	$ 2,820		$ 2,833
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	5		6
Troubled debt, balance | $	$ 427		$ 718