FHLB Advances, Other Borrowings and Subordinated Notes (Summary of Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 18, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 15, 2014
Debt Disclosure [Abstract]
FHLB advances	$ 615,000		$ 559,663	$ 468,962
Other borrowings:
Notes payable	149,799	$ 150,000	41,222	41,216	$ 150,000
Short-term borrowings	17,431		17,209	19,959
Other	48,043		49,131	49,502
Secured borrowings	158,298		158,561	141,003
Total other borrowings	373,571		266,123	251,680
Subordinated notes	139,172		139,088	139,052
Total FHLB advances, other borrowings and subordinated notes	$ 1,127,743		$ 964,874	$ 859,694