Loans Receivable and Allowance for Loan Losses (Narrative) (Details)	3 Months Ended			12 Months Ended
	Mar. 31, 2018 USD ($) SecurityLoan troubled_debt_restructuring Contract borrower	Dec. 31, 2017 USD ($) Contract	Mar. 31, 2017 USD ($) SecurityLoan	Dec. 31, 2017 USD ($) SecurityLoan Contract borrower
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount of nonaccrual loans	$ 45,900,000	$ 34,900,000		$ 34,900,000
Loans less than 90 days past due	$ 24,800,000	$ 11,500,000		$ 11,500,000
Number of loans 90 days past due and still accruing | Contract	0	0		0
Impaired loan defined floor limit (greater than)	$ 1,000,000.0
Impaired loans number | SecurityLoan	150			149
Impaired loans	$ 68,271,000	$ 52,041,000		$ 52,041,000
Number of troubled debt restructurings | troubled_debt_restructuring	127
Number of borrowers | borrower	123			121
Loans and leases receivable, impaired, nonperforming, accrual of interest	$ 37,400,000	31,700,000		$ 31,700,000
Charge off, impaired loan	$ 3,000,000		$ 0
Weighted average modified interest rate	5.66%		3.30%
Weighted average prior modification rate	5.17%		3.61%
Number of payment defaults for loans modified as TDRs | SecurityLoan	3		1
Allowances for loan losses	$ 4,548,000	2,690,000		2,690,000
Impaired financing receivable with no related allowance	30,500,000	31,400,000		31,400,000
Average balance of impaired loans	70,877,000	54,045,000
Team Capital Bank [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Balance of PCI loans	946,000	$ 1,000,000		$ 1,000,000
Impaired Loans Troubled Debt Restructurings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Allowances for loan losses	$ 411,000		$ 158,000
Impaired Loans Troubled Debt Restructurings [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of troubled debt restructurings | SecurityLoan				125