UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q þ Quarterly Report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the quarterly period ended March 31, 2019 OR ¨ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Commission file number 001-34095 FIRST BUSINESS FINANCIAL SERVICES, INC. (Exact name of registrant as specified in its charter) | --- | --- | |--------------------------------------------------------- ...