Bank subsidiary (Details 13) (USD $) In Thousands, unless otherwise specified	12 Months Ended		3 Months Ended
	Dec. 31, 2012 loan	Mar. 31, 2013	Mar. 31, 2013 Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Troubled debt restructurings that subsequently defaulted contract	Mar. 31, 2013 Residential 1-4 family Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Residential 1-4 family Troubled debt restructurings real estate loans contract	Mar. 31, 2013 Home equity line of credit Troubled debt restructurings real estate loans contract	Mar. 31, 2013 Residential land Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Residential land Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Commercial loans Troubled debt restructurings real estate loans contract	Mar. 31, 2012 Consumer loans Troubled debt restructurings that subsequently defaulted contract
Loan modifications determined to be troubled debt restructurings
Number of contracts			11	20	4	4	7	4	3	7	6	4
Pre-modification outstanding recorded investment			$ 2,508	$ 3,307		$ 1,122	$ 1,413	$ 462	$ 924	$ 1,734	$ 160
Post-modification outstanding recorded investment			2,146	3,011		1,063	1,410	215	868	1,441	160
Minimum period of payment default of loans determined to be TDRs			90 days	90 days
Recorded investment					879							879
Number of loan modified by extending maturity date	4
Commitments to borrowers whose loan terms are impaired or modified under troubled debt restructuring		$ 0