Loans and allowance for credit losses (Details 2) (USD $) | 3 Months Ended | 9 Months Ended | 12 Months Ended |
In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012 | Sep. 30, 2013 | Dec. 31, 2012 |
Unpaid principal balance | $57,927 | $105,779 | $57,927 | $105,779 |
Recorded investment with no allowance | 38,745 | 77,664 | 38,745 | 77,664 |
Recorded investment with an allowance | 9,315 | 11,163 | 9,315 | 11,163 |
Related allowance | 2,167 | 2,201 | 2,167 | 2,201 |
Average recorded investment | 68,071 | 90,193 | 75,901 | 87,064 |
Commercial Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 1,962 | 1,677 | 1,962 | 1,677 |
Recorded investment with no allowance | 647 | 715 | 647 | 715 |
Recorded investment with an allowance | 305 | 0 | 305 | 0 |
Related allowance | 305 | 0 | 305 | 0 |
Average recorded investment | 853 | 1,231 | 753 | 1,625 |
Consumer Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 87 | 92 | 87 | 92 |
Recorded investment with no allowance | 19 | 39 | 19 | 39 |
Recorded investment with an allowance | 61 | 48 | 61 | 48 |
Related allowance | 61 | 48 | 61 | 48 |
Average recorded investment | 60 | 50 | 52 | 55 |
Residential Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 24,252 | 24,992 | 24,252 | 24,992 |
Recorded investment with no allowance | 18,429 | 16,486 | 18,429 | 16,486 |
Recorded investment with an allowance | 3,742 | 2,063 | 3,742 | 2,063 |
Related allowance | 924 | 598 | 924 | 598 |
Average recorded investment | 22,131 | 19,418 | 20,154 | 22,536 |
Commercial Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 17,864 | 37,395 | 17,864 | 37,395 |
Recorded investment with no allowance | 11,264 | 29,718 | 11,264 | 29,718 |
Recorded investment with an allowance | 3,655 | 2,729 | 3,655 | 2,729 |
Related allowance | 455 | 614 | 455 | 614 |
Average recorded investment | 20,893 | 30,987 | 25,454 | 29,227 |
Construction Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 13,762 | 41,623 | 13,762 | 41,623 |
Recorded investment with no allowance | 8,386 | 30,706 | 8,386 | 30,706 |
Recorded investment with an allowance | 1,552 | 6,323 | 1,552 | 6,323 |
Related allowance | 422 | 941 | 422 | 941 |
Average recorded investment | 24,134 | 38,507 | 29,488 | 33,621 |
Impaired Nonaccrual Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 27,368 | 53,426 | 27,368 | 53,426 |
Recorded investment with no allowance | 13,054 | 25,311 | 13,054 | 25,311 |
Recorded investment with an allowance | 4,447 | 11,163 | 4,447 | 11,163 |
Related allowance | 1,135 | 2,201 | 1,135 | 2,201 |
Average recorded investment | 28,803 | 38,624 | 30,119 | 44,468 |
Impaired Nonaccrual Loans [Member] | Commercial Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 1,678 | 1,556 | 1,678 | 1,556 |
Recorded investment with no allowance | 546 | 594 | 546 | 594 |
Recorded investment with an allowance | 122 | 0 | 122 | 0 |
Related allowance | 122 | 0 | 122 | 0 |
Average recorded investment | 656 | 1,126 | 595 | 1,538 |
Impaired Nonaccrual Loans [Member] | Consumer Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 54 | 92 | 54 | 92 |
Recorded investment with no allowance | 19 | 39 | 19 | 39 |
Recorded investment with an allowance | 28 | 48 | 28 | 48 |
Related allowance | 28 | 48 | 28 | 48 |
Average recorded investment | 43 | 50 | 44 | 55 |
Impaired Nonaccrual Loans [Member] | Residential Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 7,486 | 17,975 | 7,486 | 17,975 |
Recorded investment with no allowance | 4,082 | 9,469 | 4,082 | 9,469 |
Recorded investment with an allowance | 1,323 | 2,063 | 1,323 | 2,063 |
Related allowance | 309 | 598 | 309 | 598 |
Average recorded investment | 10,825 | 13,294 | 10,921 | 17,472 |
Impaired Nonaccrual Loans [Member] | Commercial Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 6,287 | 19,515 | 6,287 | 19,515 |
Recorded investment with no allowance | 1,825 | 11,838 | 1,825 | 11,838 |
Recorded investment with an allowance | 1,517 | 2,729 | 1,517 | 2,729 |
Related allowance | 255 | 614 | 255 | 614 |
Average recorded investment | 7,607 | 13,554 | 9,905 | 12,975 |
Impaired Nonaccrual Loans [Member] | Construction Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 11,863 | 14,288 | 11,863 | 14,288 |
Recorded investment with no allowance | 6,582 | 3,371 | 6,582 | 3,371 |
Recorded investment with an allowance | 1,457 | 6,323 | 1,457 | 6,323 |
Related allowance | 421 | 941 | 421 | 941 |
Average recorded investment | 9,672 | 10,600 | 8,654 | 12,428 |
Impaired Accruing Restructured Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 29,439 | 52,353 | 29,439 | 52,353 |
Recorded investment with no allowance | 25,691 | 52,353 | 25,691 | 52,353 |
Recorded investment with an allowance | 3,748 | 0 | 3,748 | 0 |
Related allowance | 677 | 0 | 677 | 0 |
Average recorded investment | 38,706 | 51,569 | 45,502 | 42,596 |
Impaired Accruing Restructured Loans [Member] | Commercial Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 101 | 121 | 101 | 121 |
Recorded investment with no allowance | 101 | 121 | 101 | 121 |
Recorded investment with an allowance | 0 | 0 | 0 | 0 |
Related allowance | 0 | 0 | 0 | 0 |
Average recorded investment | 105 | 105 | 112 | 87 |
Impaired Accruing Restructured Loans [Member] | Consumer Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 0 | 0 | 0 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 0 | 0 | 0 | 0 |
Related allowance | 0 | 0 | 0 | 0 |
Average recorded investment | 0 | 0 | 0 | 0 |
Impaired Accruing Restructured Loans [Member] | Residential Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 16,735 | 7,017 | 16,735 | 7,017 |
Recorded investment with no allowance | 14,347 | 7,017 | 14,347 | 7,017 |
Recorded investment with an allowance | 2,388 | 0 | 2,388 | 0 |
Related allowance | 584 | 0 | 584 | 0 |
Average recorded investment | 11,290 | 6,124 | 9,225 | 5,064 |
Impaired Accruing Restructured Loans [Member] | Commercial Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 10,704 | 17,880 | 10,704 | 17,880 |
Recorded investment with no allowance | 9,439 | 17,880 | 9,439 | 17,880 |
Recorded investment with an allowance | 1,265 | 0 | 1,265 | 0 |
Related allowance | 92 | 0 | 92 | 0 |
Average recorded investment | 12,849 | 17,433 | 15,331 | 16,252 |
Impaired Accruing Restructured Loans [Member] | Construction Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 1,899 | 27,335 | 1,899 | 27,335 |
Recorded investment with no allowance | 1,804 | 27,335 | 1,804 | 27,335 |
Recorded investment with an allowance | 95 | 0 | 95 | 0 |
Related allowance | 1 | 0 | 1 | 0 |
Average recorded investment | 14,462 | 27,907 | 20,834 | 21,193 |
Impired Adversely Rated Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 1,120 | 0 | 1,120 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 1,120 | 0 | 1,120 | 0 |
Related allowance | 355 | 0 | 355 | 0 |
Average recorded investment | 562 | 0 | 280 | 0 |
Impired Adversely Rated Loans [Member] | Commercial Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 183 | 0 | 183 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 183 | 0 | 183 | 0 |
Related allowance | 183 | 0 | 183 | 0 |
Average recorded investment | 92 | 0 | 46 | 0 |
Impired Adversely Rated Loans [Member] | Consumer Loan [Member] | ' | ' | ' | ' |
Unpaid principal balance | 33 | 0 | 33 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 33 | 0 | 33 | 0 |
Related allowance | 33 | 0 | 33 | 0 |
Average recorded investment | 17 | 0 | 8 | 0 |
Impired Adversely Rated Loans [Member] | Residential Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 31 | 0 | 31 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 31 | 0 | 31 | 0 |
Related allowance | 31 | 0 | 31 | 0 |
Average recorded investment | 16 | 0 | 8 | 0 |
Impired Adversely Rated Loans [Member] | Commercial Real Estate [Member] | ' | ' | ' | ' |
Unpaid principal balance | 873 | 0 | 873 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 873 | 0 | 873 | 0 |
Related allowance | 108 | 0 | 108 | 0 |
Average recorded investment | 437 | 0 | 218 | 0 |
Impired Adversely Rated Loans [Member] | Construction Loans [Member] | ' | ' | ' | ' |
Unpaid principal balance | 0 | 0 | 0 | 0 |
Recorded investment with no allowance | 0 | 0 | 0 | 0 |
Recorded investment with an allowance | 0 | 0 | 0 | 0 |
Related allowance | 0 | 0 | 0 | 0 |
Average recorded investment | $0 | $0 | $0 | $0 |