Regulatory Capital Requirements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital Conservation Buffer	5.60%
Common Equity Tier One Capital	$ 1,317,202	$ 1,253,394
Common Equity Tier 1 Capital to Risk Weighted Assets	12.45%	12.74%
Common Equity Tier One Capital Required for Capital Adequacy	$ 476,260	$ 442,717
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 627,182
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		6.38%
Common Equity Tier One Capital Required for Capital Adequacy - minimum required plus fully phased in capital conservation buffer	$ 740,849	$ 688,670
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	7.00%	7.00%
Total Capital, Actual Amount	$ 1,439,877	$ 1,376,555
Total Capital (to risk-weighted assets), Ratio	13.60%	13.99%
Total Capital For Capital Adequacy Purposes, Amount	$ 846,685	$ 787,052
Total Capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 971,517
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		9.88%
Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 1,111,274	$ 1,033,006
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	10.50%	10.50%
Tier 1 Capital, Actual Amount	$ 1,317,202	$ 1,253,394
Tier 1 Capital (to risk-weighted assets), Ratio	12.45%	12.74%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 635,014	$ 590,289
Tier 1 Capital (to risk-weighted assets) For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 774,754
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		7.88%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 899,603	$ 836,243
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	8.50%	8.50%
Tier 1 Capital, Actual Amount	$ 1,317,202	$ 1,253,394
Tier 1 Capital (to average assets), Ratio	10.17%	10.24%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 517,938	$ 489,399
Tier 1 Capital (to average assets) For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Banking Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital Conservation Buffer	5.29%
Common Equity Tier One Capital	$ 1,318,044	$ 1,274,317
Common Equity Tier 1 Capital to Risk Weighted Assets	12.46%	12.96%
Common Equity Tier One Capital Required for Capital Adequacy	$ 475,913	$ 442,552
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier One Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 626,948
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		6.38%
Common Equity Tier One Capital Required for Capital Adequacy - minimum required plus fully phased in capital conservation buffer	$ 740,310	$ 688,414
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	7.00%	7.00%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized	$ 687,430	$ 639,241
Common Equity Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Total Capital, Actual Amount	$ 1,405,422	$ 1,362,016
Total Capital (to risk-weighted assets), Ratio	13.29%	13.85%
Total Capital For Capital Adequacy Purposes, Amount	$ 846,068	$ 786,759
Total Capital (to risk-weighted assets), For Capital Adequacy Purposes, Ratio	8.00%	8.00%
Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 971,155
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		9.88%
Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 1,110,464	$ 1,032,621
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	10.50%	10.50%
Total Capital To Be Well Capitalized Under Prompt Corrective Action Provision, Amount	$ 1,057,585	$ 983,448
Total Capital (to risk-weighted assets) To Be Well Capitalized Under Prompt Corrective Action Provision	10.00%	10.00%
Tier 1 Capital, Actual Amount	$ 1,318,044	$ 1,274,317
Tier 1 Capital (to risk-weighted assets), Ratio	12.46%	12.96%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 634,551	$ 590,069
Tier 1 Capital (to risk-weighted assets) For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer phase-in		$ 774,465
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in		7.88%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 898,947	$ 835,931
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer fully phased-in	8.50%	8.50%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Action Provision, Amount	$ 846,068	$ 786,759
Tier 1 Capital (to risk-weighted assets) To Be Well Capitalized Under Prompt Corrective Action Provision, Ratio	8.00%	8.00%
Tier 1 Capital, Actual Amount	$ 1,318,044	$ 1,274,317
Tier 1 Capital (to average assets), Ratio	10.22%	10.42%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 515,797	$ 489,254
Tier 1 Capital (to average assets) For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Capital To Be Well Capitalized Under Prompt Corrective Provision, Amount	$ 644,746	$ 611,567
Tier 1 Capital (to average assets) To Be Well Capitalized Under Prompt Corrective Provision, Ratio	5.00%	5.00%