Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended		15 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period	$ 115,554	$ 115,554	$ 109,639	$ 118,434
Established through acquisitions	0	0	8,795	0
Total goodwill, end of period	115,554	115,554	118,434	115,554
Core deposit intangible, net, beginning of period		20,166
CDI current period amortization	(1,093)	(3,362)	(3,116)	(1,177)
Total goodwill and intangible assets, end of period	132,357	132,357	139,803	132,357
Total core deposit intangible, end of period	16,803	16,803		16,803
Core Deposits [Member]
Goodwill and Intangible Assets [Line Items]
Estimated life of CDI, in years		10 years
Goodwill and Intangible Assets [Roll Forward]
Gross core deposit intangible balance, beginning of period					32,441	32,441	28,497	26,651
Accumulated amortization at beginning of period					(14,545)	(12,275)	(9,894)	(7,955)
Core deposit intangible, net, beginning of period	17,896	20,166	18,696	18,603
Established through acquisitions	0	0	5,789	3,943
CDI current period amortization	(1,093)	(3,363)	(3,116)	(1,177)
Total core deposit intangible, end of period	$ 16,803	$ 16,803	$ 21,369	$ 16,803