Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Total risk-based capital:
Actual Amount	$ 905,774us-gaap_Capital	$ 897,769us-gaap_Capital
Actual Ratio	15.40%us-gaap_CapitalToRiskWeightedAssets	16.20%us-gaap_CapitalToRiskWeightedAssets
Adequately Capitalized Amount	469,512	444,685
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	586,889	555,856
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	738,388us-gaap_TierOneRiskBasedCapital	807,229us-gaap_TierOneRiskBasedCapital
Actual Ratio	13.90%	14.50%
Adequately Capitalized Amount	352,134	222,343
Adequately Capitalized Ratio	6.00%	4.00%
Well Capitalized Amount	469,513	333,514
Well Capitalized Ratio	8.00%	6.00%
Common equity tier one risk-based capital:
Actual Amount	738,388
Actual Ratio	12.60%
Adequately Capitalized Amount	264,100
Adequately Capitalized Ratio	4.50%
Well Capitalized Amount	381,478
Well Capitalized Ratio	6.50%
Leverage capital ratio:
Actual Amount	738,388us-gaap_TierOneLeverageCapital
Actual Ratio	9.70%	9.60%
Adequately Capitalized Amount	336,536	335,897
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	420,670	419,871
Well Capitalized Ratio	5.00%	5.00%
FIB
Total risk-based capital:
Actual Amount	849,715	832,907
Actual Ratio	14.50%	15.10%
Adequately Capitalized Amount	467,636	442,468
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	584,546	553,085
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	770,619	754,708
Actual Ratio	13.20%	13.70%
Adequately Capitalized Amount	350,727	221,234
Adequately Capitalized Ratio	6.00%	4.00%
Well Capitalized Amount	467,636	331,851
Well Capitalized Ratio	8.00%	6.00%
Common equity tier one risk-based capital:
Actual Amount	770,619
Actual Ratio	13.20%
Adequately Capitalized Amount	263,046
Adequately Capitalized Ratio	4.50%
Well Capitalized Amount	379,955
Well Capitalized Ratio	6.50%
Leverage capital ratio:
Actual Amount	770,619
Actual Ratio	9.30%	9.20%
Adequately Capitalized Amount	331,521	330,006
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 414,402	$ 412,507
Well Capitalized Ratio	5.00%	5.00%

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The amount of total capital as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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