Regulatory Capital - Well Capitalized Regulatory Requirements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Actual
Common Equity Tier I Capital (to Risk-Weighted Assets)	$ 2,199,979	$ 2,011,583
Tier 1 Capital (to Risk-Weighted Assets)	2,199,979	2,011,583
Total Capital (to Risk-Weighted Assets)	2,407,976	2,197,997
Tier 1 Capital (to Average Assets)	$ 2,199,979	$ 2,011,583
Actual Ratio
Common Equity Tier I Capital (to Risk-Weighted Assets)	12.50%	12.60%
Tier 1 Capital (to Risk-Weighted Assets)	12.50%	12.60%
Total Capital (to Risk-Weighted Assets)	13.70%	13.80%
Tier 1 Capital (to Average Assets)	11.50%	11.10%
Well Capitalized Regulatory Requirements, Amount
Common Equity Tier I Capital (to Risk-Weighted Assets)	$ 1,139,897	$ 1,038,638
Tier 1 Capital (to Risk-Weighted Assets)	1,402,950	1,278,323
Total Capital (to Risk-Weighted Assets)	1,753,687	1,597,904
Tier 1 Capital (to Average Assets)	$ 955,156	$ 907,565
Well Capitalized Regulatory Requirements, Ratio
Common Equity Tier I Capital (to Risk-Weighted Assets)	6.50%	6.50%
Tier 1 Capital (to Risk-Weighted Assets)	8.00%	8.00%
Total Capital (to Risk-Weighted Assets)	10.00%	10.00%
Tier 1 Capital (to Average Assets)	5.00%	5.00%