Parent Company Information (Components of Condensed Balance Sheets The Parent Company) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 231,158	$ 190,663	$ 199,693	$ 213,914
Securities available-for-sale, at fair value	2,638,037	2,991,091
Other assets	286,677	294,462
Total assets	26,487,645	26,072,529
Liabilities and shareholders’ equity:
Total liabilities	23,785,687	23,545,517
Total liabilities and shareholders' equity	26,487,645	26,072,529
Parent Company [Member]
Assets:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	181,085	152,947	$ 279,644	$ 272,492
Intercompany debt securities	150,000	150,000
Investment in subsidiaries	2,585,955	2,425,398
Alternative investments	2,939	4,275
Other assets	13,252	24,659
Total assets	2,933,231	2,757,279
Liabilities and shareholders’ equity:
Senior notes	148,447	148,194
Junior subordinated debt	77,320	77,320
Accrued interest payable	2,616	2,589
Due to subsidiaries	575	365
Other liabilities	2,315	1,799
Total liabilities	231,273	230,267
Shareholders’ equity	2,701,958	2,527,012
Total liabilities and shareholders' equity	$ 2,933,231	$ 2,757,279