FHLB Advances, Other Borrowings and Subordinated Notes (Summary of Debt) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Disclosure [Abstract]
FHLB advances	$ 915,000	$ 559,663	$ 227,585
Other borrowings:
Notes payable	33,727	41,222	48,702
Short-term borrowings	17,977	17,209	39,246
Other	48,742	49,131	17,949
Secured borrowings	146,646	158,561	132,890
Total other borrowings	247,092	266,123	238,787
Subordinated notes	139,111	139,088	138,993
Total FHLB advances, other borrowings and subordinated notes	$ 1,301,203	$ 964,874	$ 605,365