Financial Instruments with Off-Balance Sheet Risk and Derivative Transactions - Commitments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Company's contractual commitments due to letters of credit
Total letters of credit	$ 13,071	$ 13,511
Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	233	315
Variable
Company's contractual commitments due to letters of credit
Total letters of credit	12,838	13,196
Borrower
Company's contractual commitments due to letters of credit
Total letters of credit	12,649	12,892
Borrower | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	233	220
Borrower | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	12,416	12,672
Borrower | Financial standby
Company's contractual commitments due to letters of credit
Total letters of credit	4,146	4,184
Borrower | Financial standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	167	137
Borrower | Financial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	3,979	4,047
Borrower | Commercial standby
Company's contractual commitments due to letters of credit
Total letters of credit	122	126
Borrower | Commercial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	122	126
Borrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	8,381	8,582
Borrower | Performance standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	66	83
Borrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	8,315	8,499
Nonborrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	422	619
Nonborrower | Performance standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit		95
Nonborrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	$ 422	$ 524