Acquisitions - Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands		May 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Class A common stock		$ 385,969
Goodwill			$ 445,028	$ 212,820
Cascade Bank Acquisition, as recorded by Cascade Bank
Business Acquisition [Line Items]
Cash and cash equivalents		246,804
Investment securities		476,733
Loans held for investment		2,112,077
Mortgage loans held for sale		10,253
Allowance for loan loss		(23,974)
Premises and equipment		46,554
Other real estate owned (OREO)		1,192
Core deposit intangible		0
Deferred tax assets		47,653
Other assets		98,570
Total assets acquired		3,015,862
Deposits		2,669,910
Accounts Payable and Accrued Expense		62,150
Total liabilities assumed		2,732,060
Net assets acquired		283,802
Cascade Bank Acquisition, Fair Value Adjustments
Business Acquisition [Line Items]
Cash and cash equivalents		0
Investment securities	[1]	4,876
Loans held for investment	[2]	(31,703)
Mortgage loans held for sale		6
Allowance for loan loss	[3]	23,974
Premises and equipment	[4]	178
Other real estate owned (OREO)		0
Core deposit intangible	[5]	47,968
Deferred tax assets	[6]	(21,661)
Other assets	[7]	1,136
Total assets acquired		24,774
Deposits	[8]	(934)
Accounts Payable and Accrued Expense	[9]	720
Total liabilities assumed		(214)
Net assets acquired		24,988
Cascade Bank Acquisition, as Recorded by the Company
Business Acquisition [Line Items]
Cash and cash equivalents		246,804
Investment securities		481,609
Loans held for investment		2,080,374
Mortgage loans held for sale		10,259
Allowance for loan loss		0
Premises and equipment		46,732
Other real estate owned (OREO)		1,192
Core deposit intangible		47,968
Deferred tax assets		25,992
Other assets		99,706
Total assets acquired		3,040,636
Deposits		2,668,976
Accounts Payable and Accrued Expense		62,870
Total liabilities assumed		2,731,846
Net assets acquired		308,790
Cash		155,029
Class A common stock		385,969
Total consideration paid		540,998
Goodwill		$ 232,208

[1] Write up of the book value of investments to their estimated fair values on the date of acquisition based upon quotes obtained from an independent third party pricing service.

[2] Write down of the book value of loans to their estimated fair values. Shared National Credits (SNC) were recorded at quoted sales prices where available. The fair value of the remaining loans was estimated using cash flow projections based on the remaining maturity and repricing terms, adjusted for estimated future credit losses and prepayments and discounted to present value using a risk-adjusted market rate for similar loans. The fair value of collateral dependent loans acquired with deteriorated credit quality was estimated based on the Company's analysis of the fair value of each loan's underlying collateral, discounted using market-derived rates of return with consideration given to the period of time and costs associated with foreclosure and disposition of the collateral.

[3] Adjustment to remove the Cascade allowance for loan losses at acquisition date, as the credit risk is accounted for in the fair value adjustment for loans receivable described in (2) above.

[4] Write up of the book value of premises and equipment to their estimated fair values on the date of acquisition based upon appraisals obtained from an independent third party appraiser or broker's opinion of value.

[5] Adjustment represents the value of the core deposit base assumed in the acquisition based upon valuation from an independent accounting and advisory firm.

[6] Adjustment consists of the write-off of pre-existing deferred tax assets as a result of the acquisition.

[7] Adjustment consists of various other assets recorded as a result of the acquisition, including mortgage servicing rights, SBA servicing rights, and favorable leases offset by reductions to the fair value of other items.

[8] Decrease in book value of time deposits to their estimated fair values based upon interest rates of similar time deposits with similar terms on the date of acquisition based upon valuation from an independent accounting and advisory firm.

[9] Increase in fair value due to credit card incentive program, unfavorable leases, write-off of balance sheet reserve, and swap liability offset.