Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets (Excluding Goodwill)		$ 919	$ 919	$ 919
Intangible Assets, Net (Excluding Goodwill)		58,173	17,631	23,577
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period		382,762	382,762	382,537
Established through acquisitions	[1]	383,080	0	225
Total goodwill, end of period		765,842	382,762	382,762
Core deposit intangible, net, beginning of period		17,631
CDI current period amortization		(6,333)	(5,946)	(6,882)
Total core deposit intangible, end of period		58,173	17,631
Total goodwill and intangible assets, end of period		824,015	400,393	406,339
Core Deposits [Member]
Goodwill and Intangible Assets [Roll Forward]
Gross core deposit intangible balance, beginning of period		58,598	58,598	58,598
Accumulated amortization, beginning of period		(41,886)	(35,940)	(29,058)
Core deposit intangible, net, beginning of period		16,712	22,658	29,540
Established through acquisitions		46,875	0	0
CDI current period amortization		(6,333)	(5,946)	(6,882)
Total core deposit intangible, end of period		$ 57,254	$ 16,712	$ 22,658
Estimated life of CDI, in years		10 years

[1] See Note 2, Business Combinations, for additional information regarding the goodwill related to the acquisition of Pacific Continental on November 1, 2017.