Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Total risk-based capital:
Actual Amount	$ 836,502	$ 829,443
Actual Ratio	16.80%	16.80%
Adequately Capitalized Amount	397,506	396,210
Adequately Capitalized Ratio	8.00%	8.00%
Tier 1 risk-based capital:
Actual Amount	753,154	739,246
Actual Ratio	15.20%	14.90%
Adequately Capitalized Amount	198,753	198,105
Adequately Capitalized Ratio	4.00%	4.00%
Leverage capital ratio:
Actual Ratio	10.30%	10.10%
Adequately Capitalized Amount	293,212	293,414
Adequately Capitalized Ratio	4.00%	4.00%
FIB
Total risk-based capital:
Actual Amount	728,681	723,955
Actual Ratio	14.70%	14.70%
Adequately Capitalized Amount	395,309	394,038
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	494,136	492,548
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	657,672	650,093
Actual Ratio	13.30%	13.20%
Adequately Capitalized Amount	197,654	197,019
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	296,482	295,529
Well Capitalized Ratio	6.00%	6.00%
Leverage capital ratio:
Actual Ratio	9.00%	8.90%
Adequately Capitalized Amount	291,961	292,199
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 364,952	$ 365,248
Well Capitalized Ratio	5.00%	5.00%