Loans and Allowance for Loan Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 loan	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 loan	Dec. 31, 2017 USD ($) loan
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	5	1	7	13
Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			37		40
Troubled debt, balance | $	$ 13,240		$ 13,240		$ 12,938
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			15		13
Troubled debt, balance | $	8,413		$ 8,413		$ 7,107
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			22		27
Troubled debt, balance | $	$ 4,827		$ 4,827		$ 5,831
Real estate
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		3	3
Real estate | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			25		29
Troubled debt, balance | $	$ 7,757		$ 7,757		$ 9,549
Real estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			9		8
Troubled debt, balance | $	3,683		$ 3,683		$ 4,463
Real estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			16		21
Troubled debt, balance | $	4,074		$ 4,074		$ 5,086
Real estate | Construction
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts				1
Real estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		1
Troubled debt, balance | $	490		$ 490		$ 420
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		$ 0
Real estate | Construction | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		1
Troubled debt, balance | $	490		$ 490		$ 420
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			17		19
Troubled debt, balance | $	949		$ 949		$ 1,095
Real estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			7		4
Troubled debt, balance | $	318		$ 318		$ 141
Real estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			10		15
Troubled debt, balance | $	$ 631		$ 631		$ 954
Real estate | Other commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	2		2	2
Real estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		9
Troubled debt, balance | $	$ 6,318		$ 6,318		$ 8,034
Real estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			2		4
Troubled debt, balance | $	3,365		$ 3,365		$ 4,322
Real estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			3		5
Troubled debt, balance | $	$ 2,953		$ 2,953		$ 3,712
Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3	1	3	10
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			12		11
Troubled debt, balance | $	$ 5,483		$ 5,483		$ 3,389
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		5
Troubled debt, balance | $	4,730		$ 4,730		$ 2,644
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		6
Troubled debt, balance | $	$ 753		$ 753		$ 745
Commercial | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	3	1	3	10
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			12		11
Troubled debt, balance | $	$ 5,483		$ 5,483		$ 3,389
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		5
Troubled debt, balance | $	4,730		$ 4,730		$ 2,644
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		6
Troubled debt, balance | $	$ 753		$ 753		$ 745