Recent Developments Including Mergers and Acquisitions (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 29, 2011	Jul. 12, 2011 FBC Financial Corporation [Member]	Jul. 12, 2011 1st Bank Oklahoma [Member]
Pretax gain on sale of investments	$ 4,500,000
Gain on sale of investments, Net of tax	2,600,000
Gain on sale of investments, Net of tax shares	$ 0.17
Premium paid above equity capital					1,500,000
Total assets	5,836,751,000	5,608,825,000	5,472,306,000	10,000,000,000		217,000,000
Loans	3,078,838,000	2,975,842,000	2,946,658,000			116,000,000
Deposits	5,253,505,000	5,037,735,000	4,887,332,000			178,000,000
Equity capital	$ 510,387,000	$ 483,041,000	$ 474,396,000			$ 18,000,000
Recent Transactions Including Mergers Acquisitions (Textual) [Abstract]
Interchange rate				0.21
Basis points	0.05%