Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period	$ 765,842
Total goodwill, end of period	765,842	$ 765,842
CDI current period amortization	(2,748)	(3,188)
Indefinite-lived Intangible Assets (Excluding Goodwill)	919	919
Other intangible assets, net	43,189	54,985	$ 45,937
Total goodwill and intangible assets, end of period	$ 809,031	820,827
Core Deposits [Member]
Goodwill and Intangible Assets [Line Items]
Estimated life of CDI, in years	10 years
Goodwill and Intangible Assets [Roll Forward]
Gross core deposit intangible balance, beginning of period			105,473	$ 105,473
Accumulated amortization at beginning of period			$ (60,455)	$ (48,219)
Core deposit intangible, net, beginning of period	$ 45,018	57,254
CDI current period amortization	(2,748)	(3,188)
Total core deposit intangible, end of period	$ 42,270	$ 54,066