Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Total risk-based capital:
Actual Amount	$ 931,352	$ 897,769
Actual Ratio	15.30%	16.20%
Adequately Capitalized Amount	$ 487,670	$ 444,685
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	$ 609,588	$ 555,856
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 843,096	$ 807,229
Actual Ratio	13.80%	14.50%
Adequately Capitalized Amount	$ 365,753	$ 222,343
Adequately Capitalized Ratio	6.00%	4.00%
Well Capitalized Amount	$ 487,670	$ 333,514
Well Capitalized Ratio	8.00%	6.00%
Common equity tier one risk-based capital:
Actual Amount	$ 763,096
Actual Ratio	12.50%
Adequately Capitalized Amount	$ 274,315
Adequately Capitalized Ratio	4.50%
Well Capitalized Amount	$ 396,232
Well Capitalized Ratio	6.50%
Leverage capital ratio:
Actual Amount	$ 843,096
Actual Ratio	10.10%	9.60%
Adequately Capitalized Amount	$ 332,961	$ 335,897
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 416,202	$ 419,871
Well Capitalized Ratio	5.00%	5.00%
FIB
Total risk-based capital:
Actual Amount	$ 868,800	$ 832,907
Actual Ratio	14.30%	15.10%
Adequately Capitalized Amount	$ 486,925	$ 442,468
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	$ 608,656	$ 553,085
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 788,544	$ 754,708
Actual Ratio	13.00%	13.70%
Adequately Capitalized Amount	$ 365,194	$ 221,234
Adequately Capitalized Ratio	6.00%	4.00%
Well Capitalized Amount	$ 486,925	$ 331,851
Well Capitalized Ratio	8.00%	6.00%
Common equity tier one risk-based capital:
Actual Amount	$ 788,544
Actual Ratio	13.00%
Adequately Capitalized Amount	$ 273,895
Adequately Capitalized Ratio	4.50%
Well Capitalized Amount	$ 395,626
Well Capitalized Ratio	6.50%
Leverage capital ratio:
Actual Amount	$ 788,544
Actual Ratio	9.50%	9.20%
Adequately Capitalized Amount	$ 332,071	$ 330,006
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 415,089	$ 412,507
Well Capitalized Ratio	5.00%	5.00%

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