Note 20 - Stockholders' Equity (Details) - Company's Significant Subsidiaries - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Simmons First National Corporation [Member]
Total Risk-Based Capital Ratio
Total risk-based capital, actual, amount	$ 843,227	$ 435,185
Total risk-based capital, actual, ratio	16.70%	14.50%
Total risk-based capital, minimum for capital adequacy purposes, amount	$ 403,941	$ 240,102
Total risk-based capital, minimum for capital adequacy purposes, ratio	8.00%	8.00%
Total risk-based capital, to be well capitalized under prompt corrective action provision, amount
Tier 1 Risk-Based Capital Ratio
Tier 1 risk-based capital, actual, amount	$ 808,159	$ 403,110
Tier 1 risk-based capital, actual, ratio	16.00%	13.40%
Tier 1 risk-based capital, minimum for capital adequacy purposes, amount	$ 303,060	$ 120,331
Tier 1 risk-based capital, minimum for capital adequacy purposes, ratio	6.00%	4.00%
Tier 1 risk-based capital, to be well capitalized under prompt corrective action provision, amount
Common Equity Tier 1 Capital Ratio
Common equity tier 1, actual, amount	$ 716,737
Common equity tier 1, actual, ratio	14.20%
Common equity tier 1, minimum for capital adequacy purposes, amount	$ 227,135
Common equity tier 1, minimum for capital adequacy purposes, ratio	4.50%
Common equity tier 1, to be well capitalized under prompt corrective action provision, amount
Tier 1 Leverage Ratio
Tier 1 leverage ratio, actual, amount	$ 808,159	$ 403,110
Tier 1 leverage ratio, actual, ratio	11.20%	8.80%
Tier 1 leverage ratio, minimum for capital adequacy purposes, amount	$ 288,628	$ 183,232
Tier 1 leverage ratio, minimum for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 leverage ratio, to be well capitalized under prompt corrective action provision, amount
Simmons First National Bank [Member]
Total Risk-Based Capital Ratio
Total risk-based capital, actual, amount	$ 734,170	$ 432,590
Total risk-based capital, actual, ratio	14.60%	14.50%
Total risk-based capital, minimum for capital adequacy purposes, amount	$ 402,285	$ 238,670
Total risk-based capital, minimum for capital adequacy purposes, ratio	8.00%	8.00%
Total risk-based capital, to be well capitalized under prompt corrective action provision, amount	$ 502,856	$ 298,338
Total risk-based capital, to be well capitalized under prompt corrective action provision, ratio	10.00%	10.00%
Tier 1 Risk-Based Capital Ratio
Tier 1 risk-based capital, actual, amount	$ 699,102	$ 405,834
Tier 1 risk-based capital, actual, ratio	13.90%	13.60%
Tier 1 risk-based capital, minimum for capital adequacy purposes, amount	$ 301,771	$ 119,363
Tier 1 risk-based capital, minimum for capital adequacy purposes, ratio	6.00%	4.00%
Tier 1 risk-based capital, to be well capitalized under prompt corrective action provision, amount	$ 402,361	$ 179,044
Tier 1 risk-based capital, to be well capitalized under prompt corrective action provision, ratio	8.00%	6.00%
Common Equity Tier 1 Capital Ratio
Common equity tier 1, actual, amount	$ 699,102
Common equity tier 1, actual, ratio	13.90%
Common equity tier 1, minimum for capital adequacy purposes, amount	$ 226,328
Common equity tier 1, minimum for capital adequacy purposes, ratio	4.50%
Common equity tier 1, to be well capitalized under prompt corrective action provision, amount	$ 326,918
Common equity tier 1, to be well capitalized under prompt corrective action provision, ratio	6.50%
Tier 1 Leverage Ratio
Tier 1 leverage ratio, actual, amount	$ 699,102	$ 405,834
Tier 1 leverage ratio, actual, ratio	9.70%	8.90%
Tier 1 leverage ratio, minimum for capital adequacy purposes, amount	$ 288,289	$ 182,397
Tier 1 leverage ratio, minimum for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 leverage ratio, to be well capitalized under prompt corrective action provision, amount	$ 360,362	$ 227,997
Tier 1 leverage ratio, to be well capitalized under prompt corrective action provision, ratio	5.00%	5.00%