Hedging Activities (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended		12 Months Ended
	Jun. 30, 2011 BasisPoints	Dec. 31, 2012	Mar. 31, 2012	Feb. 29, 2012	Feb. 29, 2012 Interest rate swap agreement [Member] BasisPoints	Jun. 30, 2011 Interest rate cap contracts [Member]	Dec. 31, 2012 Interest rate cap contracts [Member] Commercial Loans [Member]	Dec. 31, 2012 Mercantile Bank Prime Rate [Member]	Mar. 31, 2012 Mercantile Bank Prime Rate [Member]	Dec. 31, 2012 Wall Street Journal Prime Rate [Member] Indices	Dec. 31, 2008 Wall Street Journal Prime Rate [Member]	Oct. 31, 2008 Wall Street Journal Prime Rate [Member]
Hedging Activities (Textual) [Abstract]
Prime Rate Percentage								4.50%		3.25%
Decline in Prime Rate											0.75%	0.50%
Number of indices which likely to remain in the future period										2
Variable commercial loans percentage			47.00%						64.00%
Notional amount of purchased interest rate cap		$ 29,700,000				$ 100,000,000
Bank payment on corresponding notional amount fixed rate/ Basis for determining strike rate on purchased interest rate cap	30-Day Libor Rate				90-Day Libor Rate
Net reduction in interest income on commercial loans							254,000
Trust preferred securities interest rate index					90-Day Libor Rate
Fixed spread added to the variable rate on our trust preferred securities					218
Notional amount of interest rate swap					32,000,000
Hedging Activities (Additional Textual) [Abstract]
Strike rate of sold interest rate cap in basis points above strike rate on purchased interest rate cap	125
Notional amount of sold interest rate cap	100,000,000
Present value of purchased interest rate cap on settlement date, asset	729,500
Present value of sold interest rate cap on settlement date, liability	213,500
Payment made under interest rate cap contract		0
Trust preferred securities				32,000,000
Interest rate swap agreement maturity date		2018-01
Fair value of Interest rate swap, record as liability		1,100,000
Fair value of interest rate swap on trade date				$ 0