Goodwill and Intangible Assets (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Acquired Finite-Lived Intangible Assets [Line Items]
Amortizing the core deposit intangibles (in years)	7 years
Intangible asset amortization	$ 5,400	$ 5,300	$ 5,300
Finite-Lived Intangible Assets, Accumulated Amortization	25,800	20,400
Goodwill	59,630	59,630	59,600
Goodwill Impairment	0	$ 0	$ 0
Hillcrest Bank, N.A. [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	5,800
Bank Midwest, N.A. [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	21,700
Bank Of Choice [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	5,200
Community Banks Of Colorado [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	4,800
Pine River Bank Corporation [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 900