Parent Holding Company Information (Condensed) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Cash on hand and in banks	$ 123,270	$ 104,674
Interest bearing cash deposits	63,770	23,358
Cash and cash equivalents	187,040	128,032	105,091	210,575
Investment securities, available-for-sale	3,683,005	3,126,743
Other assets	41,969	41,709
Total assets	7,747,440	7,187,906
Liabilities and Stockholders' Equity
Subordinated debentures	125,418	125,275
Other liabilities	55,384	47,682
Total liabilities	6,846,491	6,337,679
Common stock	719	719
Paid-in capital	641,737	642,882
Retained earnings	210,531	173,139
Accumulated other comprehensive income	47,962	33,487
Total stockholders’ equity	900,949	850,227	838,204	685,890
Total liabilities and stockholders’ equity	7,747,440	7,187,906
Parent Company [Member]
Assets
Cash on hand and in banks	2,540	383
Interest bearing cash deposits	9,887	30,955
Cash and cash equivalents	12,427	31,338	29,113	18,329
Investment securities, available-for-sale	29,457	10,737
Other assets	23,221	19,041
Investment in subsidiaries	972,218	929,518
Total assets	1,037,323	990,634
Liabilities and Stockholders' Equity
Dividends Payable		9,349
Subordinated debentures	125,418	125,275
Other liabilities	10,956	5,783
Total liabilities	136,374	140,407
Common stock	719	719
Paid-in capital	641,737	642,882
Retained earnings	210,531	173,139
Accumulated other comprehensive income	47,962	33,487
Total stockholders’ equity	900,949	850,227
Total liabilities and stockholders’ equity	$ 1,037,323	$ 990,634