Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Total risk-based capital:
Actual Amount	$ 811,392	$ 748,431
Actual Ratio	16.70%	15.60%
Adequately Capitalized Amount	389,080	384,014
Adequately Capitalized Ratio	8.00%	8.00%
Tier 1 risk-based capital:
Actual Amount	722,201	652,929
Actual Ratio	14.80%	13.60%
Adequately Capitalized Amount	194,540	192,007
Adequately Capitalized Ratio	4.00%	4.00%
Leverage capital ratio:
Actual Ratio	10.00%	8.80%
Adequately Capitalized Amount	288,486	296,559
Adequately Capitalized Ratio	4.00%	4.00%
FIB
Total risk-based capital:
Actual Amount	721,266	697,695
Actual Ratio	14.90%	14.60%
Adequately Capitalized Amount	387,003	382,245
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	483,754	477,806
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	648,395	622,466
Actual Ratio	13.40%	13.00%
Adequately Capitalized Amount	193,502	191,122
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	290,252	286,683
Well Capitalized Ratio	6.00%	6.00%
Leverage capital ratio:
Actual Ratio	9.00%	8.40%
Adequately Capitalized Amount	287,443	296,061
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 359,304	$ 370,077
Well Capitalized Ratio	5.00%	5.00%