Fair Value Measurements - Nonrecurring (Details) - USD ($)		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets and liabilities measured at fair value
Valuation allowance	$ 144,000	$ 1,049,000
Increase (decrease) of specific allocations within the provision for loan losses	856,000
Carrying value of other real estate owned	8,371,000	11,916,000	$ 19,141,000	$ 31,982,000
Outstanding balance		23,500,000
OREO Valuation allowance	8,208,000	9,982,000	$ 14,127,000	$ 19,229,000
Impaired loans
Assets and liabilities measured at fair value
Valuation allowance	5,300,000
Nonrecurring
Assets and liabilities measured at fair value
Total	13,484,000	11,916,000
Nonrecurring | Impaired loans
Assets and liabilities measured at fair value
Total	5,113,000
Increase (decrease) of specific allocations within the provision for loan losses		(1)
Nonrecurring | Impaired loans | Carrying Amount
Assets and liabilities measured at fair value
Total		1,000,000
Nonrecurring | Other real estate owned
Assets and liabilities measured at fair value
Total	8,371,000	11,916,000
Outstanding balance	17,400,000
OREO Valuation allowance	8,200,000	14,100,000
OREO participations	900,000,000,000	1,700,000
Nonrecurring | Level 3
Assets and liabilities measured at fair value
Total	13,484,000	11,916,000
Nonrecurring | Level 3 | Impaired loans
Assets and liabilities measured at fair value
Total	5,113,000
Nonrecurring | Level 3 | Other real estate owned
Assets and liabilities measured at fair value
Total	$ 8,371,000	$ 11,916,000