XML 100 R84.htm IDEA: XBRL DOCUMENT v3.8.0.1
Premises and Equipment - Additional Information (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
contract
director
Dec. 31, 2016
USD ($)
director
Dec. 31, 2015
USD ($)
director
Property, Plant and Equipment [Line Items]      
Depreciation expense $ 5.1 $ 5.0 $ 4.7
Lease expiration year Jan. 01, 2054    
Capital Lease Obligations, Number of Contracts | contract 1    
Rental expense $ 4.0 $ 4.1 $ 3.9
Number of Directors | director 2 2 2
Directors      
Property, Plant and Equipment [Line Items]      
Rental expense for premises leases with two directors $ 0.2 $ 0.3 $ 0.3