XML 72 R56.htm IDEA: XBRL DOCUMENT v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
entity
unit
subsidiary
Dec. 31, 2016
USD ($)
segment
Summary of Significant Accounting Policies [Line Items]      
Number of wholly owned subsidiaries | subsidiary   3  
Percentage of outstanding common stock of investees accounted for using equity method of accounting   100.00%  
Number of entities non-banking activities | entity   5  
Number of operating segments | segment     3
Prior period reclassification adjustment   $ 0  
Period for satisfactory payment of TDRs   6 months  
Evaluation for impairment of substandard and nonaccrual commercial loans   $ 500,000  
Look-back period used for assumptions of allowance for loans and lease losses   8 years 6 months  
Number of reporting units | unit   3  
Goodwill   $ 291,670,000 $ 291,670,000
Percentage of facilities owned   55.00%  
Contractual operating lease commitments   $ 71,622,000  
Securities available-for-sale, at fair value   698,291,000 693,487,000
Equity Securities      
Summary of Significant Accounting Policies [Line Items]      
Securities available-for-sale, at fair value   $ 5,144,000 $ 11,249,000
Scenario, Forecast      
Summary of Significant Accounting Policies [Line Items]      
Provisional estimate for reclassification of AOCI to retain earnings for other income tax effects of Tax Act $ 3,200,000    
Interest rate lock commitments      
Summary of Significant Accounting Policies [Line Items]      
Period for interest rate lock commitment   60 days  
Commercial real estate      
Summary of Significant Accounting Policies [Line Items]      
Loss emergence period for used for assumptions of allowance for loans and lease losses   3 years  
Commercial construction      
Summary of Significant Accounting Policies [Line Items]      
Loss emergence period for used for assumptions of allowance for loans and lease losses   4 years  
Commercial and industrial      
Summary of Significant Accounting Policies [Line Items]      
Loss emergence period for used for assumptions of allowance for loans and lease losses   1 year 3 months  
Consumer real estate      
Summary of Significant Accounting Policies [Line Items]      
Loss emergence period for used for assumptions of allowance for loans and lease losses   2 years 9 months  
Other consumer      
Summary of Significant Accounting Policies [Line Items]      
Loss emergence period for used for assumptions of allowance for loans and lease losses   1 year 3 months  
Minimum | Core Deposits And Customers Lists      
Summary of Significant Accounting Policies [Line Items]      
Weighted average estimated useful of acquired intangibles   10 years  
Maximum      
Summary of Significant Accounting Policies [Line Items]      
Amortization period of investments in joint ventures   10 years  
Maximum | Core Deposits And Customers Lists      
Summary of Significant Accounting Policies [Line Items]      
Weighted average estimated useful of acquired intangibles   20 years  
Corporate Joint Venture | Common Wealth Trust Life Insurance Company      
Summary of Significant Accounting Policies [Line Items]      
Percentage of outstanding common stock of investees accounted for using equity method of accounting   50.00%