LHFI and Allowance for Loan Losses, LHFI - Additional Information (Details 1)	12 Months Ended
	Dec. 31, 2017 USD ($) Region	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 01, 2017 USD ($)
Financing Receivable Impaired [Line Items]
Maximum concentration of loan as a percentage of total LHFI	10.00%
Key market regions | Region	5
Loans and Leases Receivable, Related Parties	$ 59,900,000	$ 47,100,000
New loan advances to related party	418,500,000
Loan repayment by related party	405,800,000
Loan increase (decreases) from changes in executive officers and directors	12,000,000
Carrying amounts of nonaccrual LHFI considered for impairment analysis	67,600,000	49,200,000
Nonaccrual	67,575,000	49,234,000
Minimum loan amount for loan to be specifically reviewed for impairment and deemed impaired				$ 500,000
LHFI Classified as TDRs	23,900,000	14,500,000	$ 9,700,000
LHFI classified as TDRs from credits with interest only payments	20,500,000	9,800,000	5,900,000
Financing receivable, related allowance	458,000	2,200,000	1,800,000
Financing receivable, related charge-offs	127,000	1,000,000	806,000
Amount held by company of foreclosure or in substance repossession of consumer mortgage LHFI classified as TDRs	366,000	269,000
TDRs Classified as Consumer mortgage LHFI in the process of formal disclosure	0	101,000
Troubled Debt Restructurings [Member]
Financing Receivable Impaired [Line Items]
Nonaccrual	$ 23,211,000	$ 14,427,000	$ 7,418,000