Subsequent Acquisition	3 Months Ended
Mar. 31, 2019
Business Combinations [Abstract]
Subsequent Acquisition	SUBSEQUENT ACQUISITION On April 12, 2019, the Company completed its merger with Reliance Bancshares, Inc. (“Reliance”) pursuant to the terms of the Agreement and Plan of Merger (“Reliance Agreement”), dated November 13, 2018, as amended February 11, 2019. The Company was the surviving corporation in the merger. The merger was described in the Company’s Registration Statement on Form S-4 filed with the SEC on January 25, 2019, and amended on February 12, 2019. As a result of the merger, the Company expanded its presence in the St. Louis banking market and now has approximately $17.6 billion in assets and approximately $12.9 billion and $13.1 billion in loans and deposits, respectively. In the merger, each outstanding share of Reliance common stock and common stock equivalents was canceled and converted into the right to receive shares of the Company’s common stock and/or cash in accordance with the terms of the Reliance Agreement. In addition, each share of Reliance’s Series A Preferred Stock and Series B Preferred Stock was converted into the right to receive one share of Simmons’ comparable Series A Preferred Stock or Series B Preferred Stock, respectively, and each share of Reliance’s Series C Preferred Stock was converted into the right to receive one share of Simmons’ comparable Series C Preferred Stock (unless the holder of such Series C Preferred Stock elected to receive alternate consideration in accordance with the Reliance Agreement). The Company is issuing 3,999,623 shares of its common stock and paid $62.7 million in cash to effect the merger. The merger was approved by stockholders of Reliance on April 8, 2019. Due to the timing of the merger and the amount of assets and liabilities assumed, the Company is continuing to determine their preliminary fair values and the purchase price allocation. The Company expects to finalize the analysis of the acquired assets and liabilities over the next few months and within one year of the merger. The Company will record the merger using the acquisition method of accounting and will recognize the assets acquired and liabilities assumed at their fair values as of the date of acquisition. The results of the merger will be included in the Company’s consolidated operating results beginning on the acquisition date.

SUBSEQUENT ACQUISITION

On April 12, 2019, the Company completed its merger with Reliance Bancshares, Inc. (“Reliance”) pursuant to the terms of the Agreement and Plan of Merger (“Reliance Agreement”), dated November 13, 2018, as amended February 11, 2019. The Company was the surviving corporation in the merger. The merger was described in the Company’s Registration Statement on Form S-4 filed with the SEC on January 25, 2019, and amended on February 12, 2019. As a result of the merger, the Company expanded its presence in the St. Louis banking market and now has approximately $17.6 billion in assets and approximately $12.9 billion and $13.1 billion in loans and deposits, respectively.

In the merger, each outstanding share of Reliance common stock and common stock equivalents was canceled and converted into the right to receive shares of the Company’s common stock and/or cash in accordance with the terms of the Reliance Agreement. In addition, each share of Reliance’s Series A Preferred Stock and Series B Preferred Stock was converted into the right to receive one share of Simmons’ comparable Series A Preferred Stock or Series B Preferred Stock, respectively, and each share of Reliance’s Series C Preferred Stock was converted into the right to receive one share of Simmons’ comparable Series C Preferred Stock (unless the holder of such Series C Preferred Stock elected to receive alternate consideration in accordance with the Reliance Agreement). The Company is issuing 3,999,623 shares of its common stock and paid $62.7 million in cash to effect the merger. The merger was approved by stockholders of Reliance on April 8, 2019.

Due to the timing of the merger and the amount of assets and liabilities assumed, the Company is continuing to determine their preliminary fair values and the purchase price allocation. The Company expects to finalize the analysis of the acquired assets and liabilities over the next few months and within one year of the merger. The Company will record the merger using the acquisition method of accounting and will recognize the assets acquired and liabilities assumed at their fair values as of the date of acquisition. The results of the merger will be included in the Company’s consolidated operating results beginning on the acquisition date.