Parent Company (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assets:
Cash and due from banks	$ 219,256	$ 157,415
Investment securities	3,494,389	3,154,333
Loans to subsidiaries	15,629	15,723	20,126	22,005
Other assets	639,558	589,057
Total assets	14,441,702	14,134,714
Liabilities and Shareholders' Equity:
Accrued and other liabilities	12,875,749	12,626,999
Shareholders' equity	1,565,953	1,507,715	1,065,627	937,843
Total liabilities and shareholders' equity	14,441,702	14,134,714
Parent [Member]
Assets:
Cash and due from banks	61,599	9,648
Investment securities	1,385	1,340
Loans to subsidiaries	0	57,326
Investment in subsidiaries, at equity in underlying value of their net assets	1,494,442	1,431,239
Other assets	9,853	11,381
Total assets	1,567,279	1,510,934
Liabilities and Shareholders' Equity:
Accrued and other liabilities	1,326	3,219
Shareholders' equity	1,565,953	1,507,715
Total liabilities and shareholders' equity	$ 1,567,279	$ 1,510,934