Regulatory Capital Requirements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Capital	$ 1,253,394	$ 1,158,252
Capital Conservation Buffer	5.992%
Common Equity Tier 1 Capital to Risk Weighted Assets	12.7401%	11.7421%
Common Equity Tier One Capital Required for Capital Adequacy	$ 442,717	$ 443,886
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	$ 567,187
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	6.38%	5.75%
Common Equity Tier One Capital Required for Capital Adequacy - minimum required plus fully phased in capital conservation buffer	$ 688,670	$ 690,489
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	$ 1,376,555	$ 1,280,326
Total Capital (to risk-weighted assets), Ratio	13.992%	12.9796%
Total Capital For Capital Adequacy Purposes, Amount	$ 787,052	$ 789,130
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	$ 912,432
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	9.88%	9.25%
Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 1,033,006	$ 1,035,734
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	$ 1,253,394	$ 1,165,903
Tier 1 Capital (to risk-weighted assets), Ratio	12.7401%	11.8196%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 590,289	$ 591,848
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	$ 715,149
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	7.88%	7.25%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 836,243	$ 838,451
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	$ 1,253,394	$ 1,165,903
Tier 1 Capital (to average assets), Ratio	10.2444%	10.9611%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 489,399	$ 425,469
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]
Common Equity Tier One Capital	$ 1,274,317	$ 1,184,476
Capital Conservation Buffer	5.8494%
Common Equity Tier 1 Capital to Risk Weighted Assets	12.9576%	12.0133%
Common Equity Tier One Capital Required for Capital Adequacy	$ 442,552	$ 443,687
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	$ 566,933
Common Equity Tier 1 Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	6.38%	5.75%
Common Equity Tier One Capital Required for Capital Adequacy - minimum required plus fully phased in capital conservation buffer	$ 688,414	$ 690,180
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	$ 639,241	$ 640,881
Common Equity Tier 1 Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Total Capital, Actual Amount	$ 1,362,016	$ 1,263,252
Total Capital (to risk-weighted assets), Ratio	13.8494%	12.8123%
Total Capital For Capital Adequacy Purposes, Amount	$ 786,759	$ 788,777
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	$ 912,023
Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	9.88%	9.25%
Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 1,032,621	$ 1,035,269
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	$ 983,448	$ 985,971
Total Capital (to risk-weighted assets) To Be Well Capitalized Under Prompt Corrective Action Provision	10.00%	10.00%
Tier 1 Capital, Actual Amount	$ 1,274,317	$ 1,184,476
Tier 1 Capital (to risk-weighted assets), Ratio	12.9576%	12.0133%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 590,069	$ 591,582
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	$ 714,829
Tier One Based Capital Required for Capital Adequacy to Risk Weighted Assets plus capital conservation buffer phase-in	7.88%	7.25%
Tier One Risk Based Capital Required for Capital Adequacy plus capital conservation buffer fully phased-in	$ 835,931	$ 838,075
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	$ 786,759	$ 788,777
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	$ 1,274,317	$ 1,184,476
Tier 1 Capital (to average assets), Ratio	10.4185%	10.8186%
Tier 1 Capital For Capital Adequacy Purposes, Amount	$ 489,254	$ 437,939
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	$ 611,567	$ 547,423
Tier 1 Capital (to average assets) To Be Well Capitalized Under Prompt Corrective Provision, Ratio	5.00%	5.00%