Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period	$ 115,554	$ 115,554
Total goodwill, end of period	115,554
Core deposit intangible, net, beginning of period	15,721
CDI current period amortization	(1,029)	(1,150)
Total goodwill and intangible assets, end of period	130,247	134,570
Total core deposit intangible, end of period	14,693
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
Accumulated amortization at beginning of period			(16,720)	(12,275)
Core deposit intangible, net, beginning of period	15,721	20,166
CDI current period amortization	(1,028)	(1,150)
Total core deposit intangible, end of period	$ 14,693	$ 19,016