Regulatory Capital Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Total risk-based capital:
Actual Amount	$ 946,156	$ 897,769
Actual Ratio	15.40%	16.20%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 492,692
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	8.00%
Adequately Capitalized Amount	$ 646,658
Adequately Capitalized Ratio	10.50%
Well Capitalized Amount	$ 615,865	$ 555,856
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 861,339	$ 807,229
Actual Ratio	14.00%	14.50%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 369,519
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.00%
Adequately Capitalized Amount	$ 523,485
Adequately Capitalized Ratio	8.50%
Well Capitalized Amount	$ 492,692	$ 333,514
Well Capitalized Ratio	8.00%	6.00%
Common Equity Tier One Risked Based Capital	$ 781,339
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	12.70%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 383,040
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 595,840
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 400,312
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%
Leverage capital ratio:
Tier One Leverage Capital	$ 861,339	$ 807,229
Actual Ratio	10.10%	9.60%
Adequately Capitalized Amount	$ 246,346	$ 335,897
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 425,600	$ 419,871
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy		$ 444,685
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Risk Based Capital Required for Capital Adequacy		$ 222,343
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		4.00%
FIB
Total risk-based capital:
Actual Amount	$ 882,504	$ 832,907
Actual Ratio	14.40%	15.10%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 490,866
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	8.00%
Adequately Capitalized Amount	$ 644,262
Adequately Capitalized Ratio	10.50%
Well Capitalized Amount	$ 613,582	$ 553,085
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 805,805	$ 754,708
Actual Ratio	13.10%	13.70%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 368,149
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.00%
Adequately Capitalized Amount	$ 521,545
Adequately Capitalized Ratio	8.50%
Well Capitalized Amount	$ 490,866	$ 331,851
Well Capitalized Ratio	8.00%	6.00%
Common Equity Tier One Risked Based Capital	$ 805,805
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	13.10%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 381,730
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 593,802
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 398,829
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%
Leverage capital ratio:
Tier One Leverage Capital	$ 805,805	$ 754,708
Actual Ratio	9.50%	9.10%
Adequately Capitalized Amount	$ 245,433	$ 330,006
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 424,145	$ 412,507
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy		$ 442,468
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Risk Based Capital Required for Capital Adequacy		$ 221,234
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		4.00%