Loans and Allowance for Loan Losses (Details 4) (Acquired loans, USD $)										3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Mar. 31, 2013 Loans Impaired at Acquisition	Dec. 31, 2012 Loans Impaired at Acquisition	Mar. 31, 2012 Loans Impaired at Acquisition	Mar. 31, 2013 Loans Not Impaired at Acquisition	Dec. 31, 2012 Loans Not Impaired at Acquisition	Mar. 31, 2012 Loans Not Impaired at Acquisition	Mar. 31, 2013 FASB ASC Topic 310-30	Mar. 31, 2012 FASB ASC Topic 310-30	Mar. 31, 2013 FASB ASC Topic 310-30 Loans Impaired at Acquisition	Mar. 31, 2012 FASB ASC Topic 310-30 Loans Impaired at Acquisition	Mar. 31, 2013 FASB ASC Topic 310-30 Loans Not Impaired at Acquisition	Mar. 31, 2012 FASB ASC Topic 310-30 Loans Not Impaired at Acquisition	Mar. 31, 2013 FASB ASC Topic 310-20 Loans	Dec. 31, 2012 FASB ASC Topic 310-20 Loans	Mar. 31, 2012 FASB ASC Topic 310-20 Loans
Changes in the carrying value of acquired loans at the acquisition date
Balance at the beginning of the period	$ 963,978,000	$ 1,042,610,000	$ 334,789,000	$ 192,727,000	$ 216,981,000	$ 125,590,000	$ 771,251,000	$ 825,629,000	$ 209,199,000	$ 969,395,000	$ 370,581,000	$ 216,981,000	$ 146,955,000	$ 752,414,000	$ 223,626,000	$ 70,234,000	$ 73,215,000	$ 73,215,000
Net reductions for payments, foreclosures, and accretion										(76,506,000)	(33,057,000)	(22,940,000)	(19,528,000)	(53,566,000)	(13,529,000)
Change in the allowance for loan losses on acquired loans										855,000	(2,735,000)	(1,314,000)	(1,837,000)	2,169,000	(898,000)
Balance at the end of the period	963,978,000	1,042,610,000	334,789,000	192,727,000	216,981,000	125,590,000	771,251,000	825,629,000	209,199,000	893,744,000	334,789,000	192,727,000	125,590,000	701,017,000	209,199,000	70,234,000	73,215,000	73,215,000
Changes in the carrying amount of accretable difference for acquired impaired and non-impaired loans
Balance at beginning of period										160,849,000	94,600,000
Interest income										(21,712,000)	(9,110,000)
Reclass of nonaccretable difference due to improvement in expected cash flows										13,812,000	8,270,000
Other changes, net										(3,428,000)	(7,610,000)
Balance at end of period										149,521,000	86,150,000
Threshold limit for provision of specific reserve on impaired loan										250,000
Threshold limit of loans for risk assessment by loan officers										$ 500,000