Dividend Availability and Regulatory Matters Dividend Availability and Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
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	$ 2,164,152	$ 1,722,870
Tier One Leverage Capital to Average Assets	11.67%	12.34%
Tier One Leverage Capital Required to be Well Capitalized	$ 927,359	$ 698,109
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Excess Tier One Leverage Capital	$ 1,236,793	$ 1,024,761
Tier One Risk Based Common Equity	$ 2,159,741
Tier One Risk Based Common Equity to Risk Weighted Assets	12.58%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,116,069
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets	6.50%
Excess Common Equity Tier One Capital	$ 1,043,672
Tier One Risk Based Capital	$ 2,164,152	$ 1,722,870
Tier One Risk Based Capital to Risk Weighted Assets	12.60%	13.16%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,373,623	$ 785,781
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	6.00%
Excess Tier One Risk Based Capital	$ 790,529	$ 937,089
Capital	$ 2,687,377	$ 2,104,984
Capital to Risk Weighted Assets	15.65%	16.07%
Capital Required to be Well Capitalized	$ 1,717,029	$ 1,309,635
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Excess Capital	$ 970,348	$ 795,349
Pacific Western Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital	$ 2,057,546	$ 1,621,546
Tier One Leverage Capital to Average Assets	11.40%	11.70%
Tier One Leverage Capital Required to be Well Capitalized	$ 902,204	$ 693,174
Excess Tier One Leverage Capital	1,155,342	928,372
Tier One Risk Based Common Equity	$ 2,057,546
Tier One Risk Based Common Equity to Risk Weighted Assets	12.03%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,111,913
Excess Common Equity Tier One Capital	945,633
Tier One Risk Based Capital	$ 2,057,546	$ 1,621,546
Tier One Risk Based Capital to Risk Weighted Assets	12.03%	12.46%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,368,508	$ 780,834
Excess Tier One Risk Based Capital	689,038	840,712
Capital	$ 2,189,388	$ 1,712,312
Capital to Risk Weighted Assets	12.80%	13.16%
Capital Required to be Well Capitalized	$ 1,710,635	$ 1,301,390
Excess Capital	$ 478,753	$ 410,922