Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 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	765,842	$ 765,842
CDI current period amortization	(2,632)	(3,070)	(8,029)	(9,346)
Indefinite-lived Intangible Assets (Excluding Goodwill)	919	919	919	919
Other intangible assets, net	37,908	48,827	37,908	48,827		$ 45,937
Total goodwill and intangible assets, end of period	803,750	814,669	$ 803,750	814,669
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	$ 105,473	$ 105,473
Accumulated amortization at beginning of period					$ (65,852)	$ (60,455)	$ (54,495)	$ (48,219)
Core deposit intangible, net, beginning of period	39,621	50,978	$ 45,018	57,254
CDI current period amortization	(2,632)	(3,070)	(8,029)	(9,346)
Total core deposit intangible, end of period	$ 36,989	$ 47,908	$ 36,989	$ 47,908