Condensed Financial Information - Parent Company Only Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets [Abstract]
Other assets	$ 550,017	$ 527,869
Investments in:
Total Assets	17,914,718	17,124,767
Other liabilities	282,578	273,419
Total Liabilities	15,872,824	15,128,102
Shareholders' Equity [Abstract]
Shareholders’ equity	2,041,894	1,996,665	$ 2,063,187	$ 2,081,656
Total Liabilities and Shareholders’ Equity	17,914,718	17,124,767
Parent
Assets [Abstract]
Cash	0	137	$ 8	$ 40
Other assets	4,337	10,053
Receivable from subsidiaries	29,249	29,120
Investments in:
Bank subsidiaries	2,226,975	2,174,786
Non-bank subsidiaries	408,187	414,863
Total Assets	2,668,748	2,628,959
Long-term debt	361,504	465,936
Payable to non-bank subsidiaries	188,087	84,676
Other liabilities	77,263	81,682
Total Liabilities	626,854	632,294
Shareholders' Equity [Abstract]
Shareholders’ equity	2,041,894	1,996,665
Total Liabilities and Shareholders’ Equity	$ 2,668,748	$ 2,628,959