Loans and Allowance for Loan Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 loan	Dec. 31, 2017 USD ($) loan
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts	0	4	2	12
Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			37		40
Troubled debt, balance | $	$ 11,836		$ 11,836		$ 12,938
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			23		13
Troubled debt, balance | $	5,469		$ 5,469		$ 7,107
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			14		27
Troubled debt, balance | $	6,367		$ 6,367		$ 5,831
Other consumer | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Consumer
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Consumer | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Troubled debt, balance | $	91		$ 91
Consumer | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			0
Troubled debt, balance | $	0		$ 0
Consumer | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Troubled debt, balance | $	91		$ 91
Consumer | Other consumer
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Consumer | Other consumer | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, balance | $	91		$ 91
Consumer | Other consumer | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			0
Troubled debt, balance | $	0		$ 0
Consumer | Other consumer | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1
Troubled debt, balance | $	91		$ 91
Real estate
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1	3
Real estate | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			26		29
Troubled debt, balance | $	8,525		$ 8,525		$ 9,549
Real estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			18		8
Troubled debt, balance | $	4,881		$ 4,881		$ 4,463
Real estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			8		21
Troubled debt, balance | $	3,644		$ 3,644		$ 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			1		1
Troubled debt, balance | $	396		$ 396		$ 420
Real estate | Construction | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			1		0
Troubled debt, balance | $	396		$ 396		$ 0
Real estate | Construction | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			0		1
Troubled debt, balance | $	0		$ 0		$ 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 | $	967		$ 967		$ 1,095
Real estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			11		4
Troubled debt, balance | $	734		$ 734		$ 141
Real estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		15
Troubled debt, balance | $	233		$ 233		$ 954
Real estate | Other commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts				2
Real estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			8		9
Troubled debt, balance | $	7,162		$ 7,162		$ 8,034
Real estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			6		4
Troubled debt, balance | $	3,751		$ 3,751		$ 4,322
Real estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			2		5
Troubled debt, balance | $	3,411		$ 3,411		$ 3,712
Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts		4		9
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			10		11
Troubled debt, balance | $	3,220		$ 3,220		$ 3,389
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		5
Troubled debt, balance | $	588		$ 588		$ 2,644
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		6
Troubled debt, balance | $	2,632		$ 2,632		$ 745
Commercial | Commercial
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts		4		9
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			10		11
Troubled debt, balance | $	3,220		$ 3,220		$ 3,389
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		5
Troubled debt, balance | $	588		$ 588		$ 2,644
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Modifications [Line Items]
Troubled debt, number of contracts			5		6
Troubled debt, balance | $	$ 2,632		$ 2,632		$ 745