Securities - Amortized cost and fair value of available for sale securities and related pre-tax gross unrealized gains and losses (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 130,370,000	$ 134,664,000
Gross Unrealized Gains	1,977,000	4,038,000
Gross Unrealized Losses	(8,554,000)	(388,000)
Fair Value	123,793,000	138,314,000
U.S. Government agency debt obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	97,460,000	78,447,000
Gross Unrealized Gains	376,000	1,039,000
Gross Unrealized Losses	(8,542,000)	(388,000)
Fair Value	89,294,000	79,098,000
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,382,000	20,182,000
Gross Unrealized Gains	1,129,000	1,814,000
Gross Unrealized Losses	0	0
Fair Value	14,511,000	21,996,000
Michigan Strategic Fund bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	11,255,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	11,255,000
Municipal general obligation bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,275,000	21,700,000
Gross Unrealized Gains	432,000	1,043,000
Gross Unrealized Losses	(1,000)	0
Fair Value	17,706,000	22,743,000
Municipal revenue bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	877,000	1,726,000
Gross Unrealized Gains	40,000	91,000
Gross Unrealized Losses	0	0
Fair Value	917,000	1,817,000
Mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,376,000	1,354,000
Gross Unrealized Gains	0	51,000
Gross Unrealized Losses	(11,000)	0
Fair Value	$ 1,365,000	$ 1,405,000