Securities (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011 item
Securities
Number of securities held with unrealized loss	41	36
Proceeds from sales of securities available-for-sale	$ 60,318,000
Gross realized gains from sale of available for sale securities	8,477,000
Total available-for-sale securities	336,300,000	344,187,000
Held-to-maturity, amortized cost	1,700,141,000	2,130,804,000
Held-to-maturity, Estimated fair value	1,725,090,000	2,176,925,000
Accrued interest receivable for securities	5,700,000	7,500,000
Callable securities, amortized cost	98,700,000
Held-to-maturity debt securities, excluding mortgage-backed securities
Securities
Held-to-maturity, amortized cost	656,000
Held-to-maturity, Estimated fair value	656,000
Available-for-sale debt securities, excluding mortgage-backed securities
Securities
Available-for-sale debt securities, amortized cost	98,700,000
Total available-for-sale securities	$ 98,900,000