Consideration Transferred, Identifiable Net Assets Acquired and Goodwill Recognized (Details) - USD ($)						12 Months Ended
		Jul. 31, 2019	Apr. 30, 2019	Feb. 28, 2018	Jan. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value of consideration transferred
Effective settlement of pre-existing receivable						$ 0	$ 10,054,000	$ 0
Liabilities assumed
Goodwill recognized						$ 166,832,000	$ 111,775,000	$ 30,758,000
Heritage Bank
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs		$ 229,385,000
Cash consideration for outstanding shares		16,420,000
Effective settlement of pre-existing receivable		0
Total fair value of consideration transferred		245,805,000
Identifiable assets acquired
Cash and cash equivalents		84,446,000
Debt securities		103,231,000
Loans receivable		615,279,000
Core deposit intangible	[1]	13,566,000
Accrued income and other assets		35,891,000
Total identifiable assets acquired		852,413,000
Liabilities assumed
Deposits		722,220,000
Borrowings		0
Accrued expenses and other liabilities		9,919,000
Total liabilities assumed		732,139,000
Total identifiable net assets		120,274,000
Goodwill recognized		$ 125,531,000
Core Deposit Intangible, Weighted Average Useful Life		10 years
First Community Bank Utah
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs			$ 87,153,000
Cash consideration for outstanding shares			4,000
Effective settlement of pre-existing receivable			0
Total fair value of consideration transferred			87,157,000
Identifiable assets acquired
Cash and cash equivalents			11,311,000
Debt securities			47,247,000
Loans receivable			245,485,000
Core deposit intangible	[1]		8,963,000
Accrued income and other assets			24,848,000
Total identifiable assets acquired			337,854,000
Liabilities assumed
Deposits			274,646,000
Borrowings			7,273,000
Accrued expenses and other liabilities			10,079,000
Total liabilities assumed			291,998,000
Total identifiable net assets			45,856,000
Goodwill recognized			$ 41,301,000
Core Deposit Intangible, Weighted Average Useful Life			10 years
First Security Bank
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs				$ 181,043,000
Cash consideration for outstanding shares				0
Effective settlement of pre-existing receivable				0
Total fair value of consideration transferred				181,043,000
Identifiable assets acquired
Cash and cash equivalents				24,397,000
Debt securities				271,865,000
Loans receivable				627,767,000
Core deposit intangible	[1]			31,053,000
Accrued income and other assets				78,274,000
Total identifiable assets acquired				1,033,356,000
Liabilities assumed
Deposits				877,586,000
Borrowings	[2]			36,880,000
Accrued expenses and other liabilities				14,175,000
Total liabilities assumed				928,641,000
Total identifiable net assets				104,715,000
Goodwill recognized				$ 76,328,000
Core Deposit Intangible, Weighted Average Useful Life				10 years
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Subordinated Debentures				$ 5,864,000
Collegiate Peaks Bank
Fair value of consideration transferred
Fair value of Company shares issued, net of equity issuance costs					$ 69,764,000
Cash consideration for outstanding shares					16,265,000
Effective settlement of pre-existing receivable					10,054,000
Total fair value of consideration transferred					96,083,000
Identifiable assets acquired
Cash and cash equivalents					93,136,000
Debt securities					42,177,000
Loans receivable					354,252,000
Core deposit intangible	[1]				10,275,000
Accrued income and other assets					15,911,000
Total identifiable assets acquired					515,751,000
Liabilities assumed
Deposits					437,171,000
Borrowings					12,509,000
Accrued expenses and other liabilities					5,435,000
Total liabilities assumed					455,115,000
Total identifiable net assets					60,636,000
Goodwill recognized					$ 35,447,000
Core Deposit Intangible, Weighted Average Useful Life					10 years

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

[2] Borrowings assumed with the FSB acquisition included Tier 2 subordinated debentures of $5,864,000.