Dividend Availability and Regulatory Matters Dividend Availability and Regulatory Matters (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital	$ 2,403,721	$ 2,306,966
Tier One Leverage Capital to Average Assets	8.55%	9.74%
Tier One Leverage Capital Required to be Well Capitalized	$ 1,404,880	$ 1,184,347
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets Capital Conservation Buffer	4.00%	4.00%
Tier One Risk Based Common Equity	$ 2,403,721	$ 2,306,966
Tier One Risk Based Common Equity to Risk Weighted Assets	10.53%	9.78%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,484,450	$ 1,532,971
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	7.00%	7.00%
Tier One Risk Based Capital	$ 2,403,721	$ 2,306,966
Tier One Risk Based Capital to Risk Weighted Assets	10.53%	9.78%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,827,015	$ 1,886,734
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	8.50%	8.50%
Capital	$ 3,141,992	$ 2,926,075
Capital to Risk Weighted Assets	13.76%	12.41%
Capital Required to be Well Capitalized	$ 2,283,769	$ 2,358,417
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Capital Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	10.50%	10.50%
Pacific Western Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital	$ 2,673,960	$ 2,589,473
Tier One Leverage Capital to Average Assets	9.53%	10.95%
Tier One Leverage Capital Required to be Well Capitalized	$ 1,403,208	$ 1,182,683
Tier One Leverage Capital Required to be Well Capitalized to Average Assets		5.00%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets Capital Conservation Buffer	4.00%	4.00%
Tier One Risk Based Common Equity	$ 2,673,960	$ 2,589,473
Tier One Risk Based Common Equity to Risk Weighted Assets	11.73%	11.00%
Tier One Risk Based Common Equity Required to be Well Capitalized	$ 1,481,599	$ 1,530,088
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets		6.50%
Tier One Risk Based Common Equity Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	7.00%	7.00%
Tier One Risk Based Capital	$ 2,673,960	$ 2,589,473
Tier One Risk Based Capital to Risk Weighted Assets	11.73%	11.00%
Tier One Risk Based Capital Required to be Well Capitalized	$ 1,823,506	$ 1,883,185
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		8.00%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	8.50%	8.50%
Capital	$ 2,959,853	$ 2,764,128
Capital to Risk Weighted Assets	12.99%	11.74%
Capital Required to be Well Capitalized	$ 2,279,383	$ 2,353,981
Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%
Capital Required to be Well Capitalized to Risk Weighted Assets Capital Conservation Buffer	10.50%	10.50%