Derivative Financial Instruments - Interest Swap Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value	$ 264,474		$ 174,359
Interest expense	10,564	$ 5,933
Interest rate swaps | Derivatives designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value	$ 360,609		$ 141,135
Weighted Average Remaining Maturity (years)	6 years 8 months 12 days		7 years 6 months
Fair Value	$ 1,555		$ (271)
Weighted-Average Rate	2.71%		2.41%
Cash collateral received			$ 1,600
Cash collateral pledged			700
Interest expense	$ 100	$ 0
Loans | Derivatives designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value	(676)		263
Loans | Interest rate swaps | Derivatives designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value	$ 272,409		$ 91,135
Weighted Average Remaining Maturity (years)	7 years		7 years 10 months 24 days
Fair Value	$ 676		$ (263)
Weighted-Average Rate	2.77%		2.44%
Securities available-for-sale | Derivatives designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value	$ (876)		$ 8
Securities available-for-sale | Interest rate swaps | Derivatives designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value	$ 88,200		$ 50,000
Weighted Average Remaining Maturity (years)	5 years 10 months 24 days		6 years 9 months 18 days
Fair Value	$ 879		$ (8)
Weighted-Average Rate	2.54%		2.33%