Fair Value Measurement of Assets and Liabilities - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value Assets Measured On Recurring Basis
Impaired collateral dependent loans, charge-offs		$ 1,900,000		$ 2,100,000
Collateral dependent impaired loans, recorded investment	$ 60,300,000		$ 60,300,000
Specific valuation allowance allocations	23,300,000		23,300,000
Reported net carrying amount of impaired loans	37,000,000		$ 37,000,000
Valuation of loan servicing rights, discount rate			8.00%
Net impairment charges (recoveries) on its loan servicing rights	(90,000)	(50,000)	$ (317,000)	(51,000)
Foreclosed assets measured at fair value upon initial recognition			1,200,000
Foreclosed asset charge-offs	649,000	282,000	1,200,000	994,000
Loss due to re-measurement of repossessed assets			$ 145,000	290,000
Minimum
Fair Value Assets Measured On Recurring Basis
Valuation of loan servicing rights, prepayment rate			0.00%
Maximum
Fair Value Assets Measured On Recurring Basis
Valuation of loan servicing rights, prepayment rate			24.00%
Available for Sale Securities
Fair Value Assets Measured On Recurring Basis
Changes in unrealized losses on Level 3 securities	$ 0	$ 0		$ 0