Note 9 - Stock-based Compensation (Details) (USD $)	0 Months Ended	6 Months Ended	12 Months Ended									6 Months Ended	12 Months Ended		6 Months Ended	12 Months Ended				6 Months Ended				6 Months Ended		0 Months Ended	6 Months Ended			12 Months Ended			6 Months Ended	12 Months Ended			1 Months Ended
	Jun. 26, 2014	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2005	Dec. 31, 2012 Restricted Stock [Member] Stock Incentive Plan of 2006 [Member]	Dec. 31, 2008 Restricted Stock [Member] Stock Incentive Plan of 2006 [Member]	Dec. 31, 2007 Restricted Stock [Member] Stock Incentive Plan of 2006 [Member]	Dec. 31, 2006 Restricted Stock [Member] Stock Incentive Plan of 2006 [Member]	Jun. 30, 2014 Restricted Stock [Member] Mercantile Plans [Member]	Dec. 31, 2013 Restricted Stock [Member] Mercantile Plans [Member]	Dec. 31, 2012 Restricted Stock [Member] Mercantile Plans [Member]	Jun. 30, 2014 Restricted Stock [Member]	Dec. 31, 2013 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	Dec. 31, 2009 Restricted Stock [Member]	Jun. 30, 2014 Grants of Less Than 50 Shares [Member] Firstbank Corporation [Member]	Jun. 30, 2014 Grants of More Than 50 Shares [Member] Firstbank Corporation [Member]	Jun. 30, 2014 Firstbank Corporation [Member]	Jun. 01, 2014 Firstbank Corporation [Member]	Jun. 30, 2014 Firstbank Corporation [Member] Minimum [Member]	Jun. 30, 2014 Firstbank Corporation [Member] Maximum [Member]	Jun. 26, 2014 Director [Member]	Jun. 30, 2014 2000 Employee Stock Option Plan [Member]	Jun. 30, 2014 2004 Employee Stock Option Plan [Member]	Jun. 30, 2014 Independent Director Stock Plan [Member]	Dec. 31, 2008 Stock Incentive Plan of 2006 [Member]	Dec. 31, 2007 Stock Incentive Plan of 2006 [Member]	Dec. 31, 2006 Stock Incentive Plan of 2006 [Member]	Jun. 30, 2014 Mercantile Plans [Member]	Dec. 31, 2013 Mercantile Plans [Member]	Dec. 31, 2012 Mercantile Plans [Member]	Dec. 31, 2011 Mercantile Plans [Member]	Jun. 30, 2014 Firstbank Plans [Member]	May 31, 2014 Firstbank Plans [Member]
Note 9 - Stock-based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares)		0	0	0	0	0																											0	0	0		0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares)												0	0	66,100	0	0	0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							21 days	2 years	4 years	4 years	4 years									1 year	5 years			6 months	18 months		1 year	1 year	5 years	2 years	2 years	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period																						10 years					10 years	10 years	10 years	7 years	7 years	7 years
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent																													125.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in Shares)			384,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized (in Dollars)		$ 200,000
Share-based Compensation Arrangement by Share-based Payment Award, Option Grant Vesting Threshold (in Shares)																						50
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage																					20.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number (in Shares)																							282,200										56,890	60,876	152,896	214,903	279,103	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in Shares)																							258,400										56,890	60,876	152,896		255,373
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in Shares)																						23,800
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options (in Dollars)																						100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value (in Dollars)																																	100,000				2,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value (in Dollars)																																	100,000				2,100,000
Stock Issued During Period, Shares, Issued for Services (in Shares)	7,375
Deferred Compensation Arrangement with Individual, Allocated Share-based Compensation Expense (in Dollars)																										$ 155,000