Mergers and Acquisitions - Consideration Transferred, Identifiable Net Assets Acquired and Goodwill Recognized (Details) - USD ($) $ in Thousands					12 Months Ended
		Feb. 29, 2020	Jul. 31, 2019	Apr. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liabilities assumed
Goodwill recognized					$ 57,595	$ 166,832	$ 111,775
State Bank of Arizona
Fair value of consideration transferred
Fair value of Company shares issued		$ 112,133
Cash consideration		13,721
Total fair value of consideration transferred		125,854
Identifiable assets acquired
Cash and cash equivalents		57,434
Debt securities		142,174
Loans receivable, net of ACL		451,653
Core deposit Intangible	[1]	2,593
Accrued income and other assets		33,971
Total identifiable assets acquired		687,825
Liabilities assumed
Deposits		603,289
Borrowings		10,904
Accrued expenses and other liabilities		5,373
Total liabilities assumed		619,566
Total identifiable net assets		68,259
Goodwill recognized		$ 57,595
Heritage Bank
Fair value of consideration transferred
Fair value of Company shares issued			$ 229,385
Cash consideration			16,420
Total fair value of consideration transferred			245,805
Identifiable assets acquired
Cash and cash equivalents			84,446
Debt securities			103,231
Loans receivable, net of ACL			615,279
Core deposit Intangible	[1]		13,566
Accrued income and other assets			35,891
Total identifiable assets acquired			852,413
Liabilities assumed
Deposits			722,220
Borrowings			0
Accrued expenses and other liabilities			9,919
Total liabilities assumed			732,139
Total identifiable net assets			120,274
Goodwill recognized			$ 125,531
Core deposit intangible, weighted average useful life (in years)			10 years
First Community Bank Utah
Fair value of consideration transferred
Fair value of Company shares issued				$ 87,153
Cash consideration				4
Total fair value of consideration transferred				87,157
Identifiable assets acquired
Cash and cash equivalents				11,311
Debt securities				47,247
Loans receivable, net of ACL				245,485
Core deposit Intangible	[1]			8,963
Accrued income and other assets				24,848
Total identifiable assets acquired				337,854
Liabilities assumed
Deposits				274,646
Borrowings				7,273
Accrued expenses and other liabilities				10,079
Total liabilities assumed				291,998
Total identifiable net assets				45,856
Goodwill recognized				$ 41,301
Core deposit intangible, weighted average useful life (in years)			10 years

[1] The core deposit intangible for each acquisition was determined to have an estimated life of 10 years.