Commitments, Contingencies and Concentrations of Risk (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employment Agreements
Rental expense	$ 4.8	$ 4.4	$ 3.8
CEO | Employment Agreements
Employment Agreements
Term of agreements (in years)	3 years
Chief Banking Officer | Employment Agreements
Employment Agreements
Term of agreements (in years)	3 years
Chief Financial Officer | Employment Agreements
Employment Agreements
Term of agreements (in years)	3 years
Chief Credit Officer | Employment Agreements
Employment Agreements
Term of agreements (in years)	3 years