Available-for-Sale and Held-to-Maturity Securities (Narrative) (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010	Dec. 31, 2010
Available-for-sale securities, par value	$ 30,000,000			$ 43,000,000
Gains or losses recorded in consolidated statement of operations	0			0
Principal payments on mortgage-backed securities	62,800,000			121,200,000
Carrying value of municipal auction rate securities from held-to-maturity to available-for-sale	27,800,000
Securities available for sale to securities held to maturity	64,600,000
Unrealized gains, net of deferred taxes	5,400,000		4,200,000	6,600,000		7,500,000
Carrying value of securities pledged as collateral	121,000,000			121,000,000			111,600,000
Available-for-sale securities, Estimated fair value	1,074,114,000			1,074,114,000			1,012,714,000
Available-for-sale securities, percentage of investment portfolio	17.70%			17.70%
Available-for-sale Securities, Amortized cost	1,056,867,000			1,056,867,000			1,005,657,000
Credit-related other-than-temporary impairment	1,500,000			1,900,000
Gross unrealized losses related to all other securities	3,631,000	[1]		3,631,000	[1]		5,004,000	[1]
Available-for-sale Securities [Member]
Available-for-sale securities, Estimated fair value	190,200,000			190,200,000
Available-for-sale Securities, Amortized cost	$ 193,800,000			$ 193,800,000

[1] Unrealized gains/(losses) related to available-for-sale securities are reported in accumulated other comprehensive income.