Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period				$ 765,842
Total goodwill, end of period	$ 765,842	[1]	$ 382,762	765,842	[1]	$ 382,762
CDI current period amortization	(3,070)		(1,188)	(9,346)		(3,786)
Indefinite-lived Intangible Assets (Excluding Goodwill)	919		919	919		919
Other intangible assets, net	48,827		13,845	48,827		13,845		$ 58,173
Total goodwill and intangible assets, end of period	814,669		396,607	$ 814,669		396,607
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	$ 58,598	$ 58,598
Accumulated amortization at beginning of period							$ (54,495)	$ (48,219)	$ (44,484)	$ (41,886)
Core deposit intangible, net, beginning of period	50,978		14,114	$ 57,254		16,712
CDI current period amortization	(3,070)		(1,188)	(9,346)		(3,786)
Total core deposit intangible, end of period	$ 47,908		$ 12,926	$ 47,908		$ 12,926

[1] See Note 3, “Business Combinations,” for additional information regarding goodwill and intangible assets recorded related to the acquisition of Pacific Continental on November 1, 2017.