Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Total risk-based capital:
Actual Amount	$ 790,896	$ 800,354
Actual Ratio	16.50%	16.50%
Adequately Capitalized Amount	382,980	387,082
Adequately Capitalized Ratio	8.00%	8.00%
Tier 1 risk-based capital:
Actual Amount	695,572	704,229
Actual Ratio	14.50%	14.60%
Adequately Capitalized Amount	191,490	193,541
Adequately Capitalized Ratio	4.00%	4.00%
Leverage capital ratio:
Actual Ratio	9.60%	9.80%
Adequately Capitalized Amount	291,093	286,303
Adequately Capitalized Ratio	4.00%	4.00%
FIB
Total risk-based capital:
Actual Amount	687,085	663,860
Actual Ratio	14.40%	13.80%
Adequately Capitalized Amount	381,297	384,987
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	476,621	481,234
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	612,021	588,059
Actual Ratio	12.80%	12.20%
Adequately Capitalized Amount	190,648	192,494
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	285,973	288,740
Well Capitalized Ratio	6.00%	6.00%
Leverage capital ratio:
Actual Ratio	8.40%	8.20%
Adequately Capitalized Amount	290,214	285,358
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 362,768	$ 356,698
Well Capitalized Ratio	5.00%	5.00%