Dividend Availability and Regulatory Matters Dividend Availability and Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%
Tier One Leverage Capital	$ 2,286,203	$ 2,164,152
Tier One Leverage Capital to Average Assets	11.40%	11.40%
Tier One Leverage Capital Required to be Well Capitalized	$ 959,477	$ 927,359
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Excess Tier One Leverage Capital	$ 1,326,726	$ 1,236,793
Tier One Risk Based Common Equity	$ 2,286,203	$ 2,159,741
Tier One Risk Based Common Equity to Risk Weighted Assets	11.78%	12.03%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,206,960	$ 1,116,069
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Excess Common Equity Tier One Capital	$ 1,079,243	$ 1,043,672
Tier One Risk Based Capital	$ 2,286,203	$ 2,164,152
Tier One Risk Based Capital to Risk Weighted Assets	11.78%	12.03%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,485,490	$ 1,373,623
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Excess Tier One Risk Based Capital	$ 800,713	$ 790,529
Capital	$ 2,889,163	$ 2,687,377
Capital to Risk Weighted Assets	12.72%	12.80%
Capital Required to be Well Capitalized	$ 1,856,862	$ 1,717,029
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Excess Capital	$ 1,032,301	$ 970,348
Pacific Western Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital	$ 2,184,097	$ 2,057,546
Tier One Leverage Capital to Average Assets	11.91%	11.67%
Tier One Leverage Capital Required to be Well Capitalized	$ 957,630	$ 902,204
Excess Tier One Leverage Capital	1,226,467	1,155,342
Tier One Risk Based Common Equity	$ 2,184,097	$ 2,057,546
Tier One Risk Based Common Equity to Risk Weighted Assets	12.31%	12.58%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,205,541	$ 1,111,913
Excess Common Equity Tier One Capital	978,556	945,633
Tier One Risk Based Capital	$ 2,184,097	$ 2,057,546
Tier One Risk Based Capital to Risk Weighted Assets	12.31%	12.60%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,483,742	$ 1,368,508
Excess Tier One Risk Based Capital	700,355	689,038
Capital	$ 2,358,829	$ 2,189,388
Capital to Risk Weighted Assets	15.56%	15.65%
Capital Required to be Well Capitalized	$ 1,854,678	$ 1,710,635
Excess Capital	$ 504,151	$ 478,753