Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Total risk-based capital:
Actual Amount	$ 1,086,842	$ 974,488
Actual Ratio	12.56%	15.13%
Well Capitalized Amount	$ 865,061	$ 643,876
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 1,011,141	$ 894,273
Actual Ratio	11.69%	13.89%
Well Capitalized Amount	$ 692,049	$ 515,101
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 931,675	$ 814,273
Actual Ratio	10.77%	12.65%
Leverage capital ratio:
Actual Amount	$ 1,011,141	$ 894,273
Actual Ratio	10.65%	10.11%
Adequately Capitalized Amount	$ 379,616	$ 353,838
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 474,519	$ 442,297
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 800,182	$ 555,665
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.25%	8.63%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 908,314	$ 676,070
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	10.50%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 627,169	$ 426,890
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.25%	6.63%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 735,302	$ 547,295
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	8.50%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 497,410	$ 330,308
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	5.75%	5.13%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 605,543	$ 450,713
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 562,290	$ 418,519
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
FIB
Total risk-based capital:
Actual Amount	$ 824,454	$ 841,967
Actual Ratio	13.00%	13.13%
Well Capitalized Amount	$ 634,208	$ 641,320
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 748,753	$ 765,753
Actual Ratio	11.81%	11.94%
Well Capitalized Amount	$ 507,366	$ 513,056
Well Capitalized Ratio	8.00%	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 748,753	$ 765,753
Actual Ratio	11.81%	11.94%
Leverage capital ratio:
Actual Amount	$ 748,753	$ 765,753
Actual Ratio	8.67%	8.69%
Adequately Capitalized Amount	$ 345,442	$ 352,283
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 431,803	$ 440,353
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 586,642	$ 553,459
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.25%	8.63%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 665,918	$ 673,386
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%	10.50%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 459,801	$ 425,195
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.25%	6.63%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 539,077	$ 545,122
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%	8.50%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 364,669	$ 328,997
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	5.75%	5.13%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 443,945	$ 448,924
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 412,235	$ 416,858
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Bank of the Cascades [Member]
Total risk-based capital:
Actual Amount	$ 240,391
Actual Ratio	10.53%
Well Capitalized Amount	$ 228,265
Well Capitalized Ratio	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 240,391
Actual Ratio	10.53%
Well Capitalized Amount	$ 182,612
Well Capitalized Ratio	8.00%
Common equity tier one risk-based capital:
Actual Amount	$ 240,391
Actual Ratio	10.53%
Leverage capital ratio:
Actual Amount	$ 240,391
Actual Ratio	8.12%
Adequately Capitalized Amount	$ 118,476
Adequately Capitalized Ratio	4.00%
Well Capitalized Amount	$ 148,095
Well Capitalized Ratio	5.00%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 211,145
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	9.25%
Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 239,678
Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	10.50%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 165,492
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	7.25%
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 194,025
Tier One Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	8.50%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 131,252
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	5.75%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 159,786
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 148,372
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%