Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended			3 Months Ended
	Mar. 31, 2012	Feb. 29, 2012	Jan. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Components of AOCI
Net unrealized gain on securities available-for-sale	$ 81,162			$ 81,162	$ 73,235
Net unrealized gain on cash flow hedges	180			180	222
Pension liability adjustment					(1,085)
Total accumulated other comprehensive income	$ 81,342			$ 81,342	$ 72,372
Common shares repurchased
Total number of Shares (or Units) Purchased	13,817	25,029	148	38,994
Average Price Paid per Share (or Unit) (in dollars per share)	$ 46.12	$ 47.69	$ 48.86	$ 47.14
Shares of common stock reserved for issuance (in shares)	1,100,000			1,100,000
Shares of unvested restricted stock (in shares)	600,000			600,000