Borrowings - Customer Repurchase Agreements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Customer repurchase agreements
Balance	$ 96,282	$ 109,740	$ 90,271
Weighted average interest rate at year end	0.07%	0.20%	0.30%
Maximum amount outstanding at any month's end	117,291	111,724	109,712
Average amount outstanding during the year	$ 106,206	$ 102,873	$ 97,667
Weighted average interest rate during the year	0.13%	0.28%	0.40%