Goodwill and Intangible Assets (Schedule of Goodwill and Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Goodwill and Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets (Excluding Goodwill)	$ 919	$ 919		$ 919
Intangible Assets, Net (Excluding Goodwill)	17,631	23,577		30,459
Goodwill and Intangible Assets [Roll Forward]
Total goodwill, beginning of period	382,762	382,537		343,952
Established through acquisitions	0	225	[1]	38,585	[1]
Total goodwill, end of period	382,762	382,762		382,537
Core deposit intangible, net, beginning of period	23,577
CDI current period amortization	(5,946)	(6,882)		(6,293)
Total core deposit intangible, end of period	17,631	23,577
Total goodwill and intangible assets, end of period	400,393	406,339		412,996
Core Deposits [Member]
Goodwill and Intangible Assets [Roll Forward]
Gross core deposit intangible balance, beginning of period	58,598	58,598		47,698
Accumulated amortization, beginning of period	(35,940)	(29,058)		(22,765)
Core deposit intangible, net, beginning of period	22,658	29,540		24,933
Established through acquisitions	0	0		10,900
CDI current period amortization	(5,946)	(6,882)		(6,293)
Total core deposit intangible, end of period	$ 16,712	$ 22,658		$ 29,540
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 Intermountain on November 1, 2014