Dividend Availability and Regulatory Matters Dividend Availability and Regulatory Matters (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital Conservation Buffer Percentage		2.50%	1.875%
Tier One Leverage Capital		$ 2,306,966	$ 2,255,588
Tier One Leverage Capital to Average Assets		9.74%	10.13%
Tier One Leverage Capital Required to be Well Capitalized		$ 1,184,347	$ 1,113,341
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	[1]	4.00%	4.00%
Tier One Risk Based Common Equity		$ 2,306,966	$ 2,255,588
Tier One Risk Based Common Equity to Risk Weighted Assets		9.78%	10.01%
Tier One Risk Based Common Equity Required to be Well Capitalized		$ 1,532,971	$ 1,464,131
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	[1]	7.00%	6.375%
Tier One Risk Based Capital		$ 2,306,966	$ 2,255,588
Tier One Risk Based Capital to Risk Weighted Assets		9.78%	10.01%
Tier One Risk Based Capital Required to be Well Capitalized		$ 1,886,734	$ 1,802,008
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	[1]	8.50%	7.875%
Capital		$ 2,926,075	$ 2,865,152
Capital to Risk Weighted Assets		12.41%	12.72%
Capital Required to be Well Capitalized		$ 2,358,417	$ 2,252,510
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	[1]	10.50%	9.875%
Pacific Western Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier One Leverage Capital		$ 2,589,473	$ 2,403,244
Tier One Leverage Capital to Average Assets		10.95%	10.80%
Tier One Leverage Capital Required to be Well Capitalized		$ 1,182,683	$ 1,112,356
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	[1]	4.00%	4.00%
Tier One Risk Based Common Equity		$ 2,589,473	$ 2,403,244
Tier One Risk Based Common Equity to Risk Weighted Assets		11.00%	10.68%
Tier One Risk Based Common Equity Required to be Well Capitalized		$ 1,530,088	$ 1,462,083
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	[1]	7.00%	6.375%
Tier One Risk Based Capital		$ 2,589,473	$ 2,403,244
Tier One Risk Based Capital to Risk Weighted Assets		11.00%	10.68%
Tier One Risk Based Capital Required to be Well Capitalized		$ 1,883,185	$ 1,799,487
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	[1]	8.50%	7.875%
Capital		$ 2,764,128	$ 2,572,586
Capital to Risk Weighted Assets		11.74%	11.44%
Capital Required to be Well Capitalized		$ 2,353,981	$ 2,249,359
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	[1]	10.50%	9.875%

[1] Ratios for December 31, 2019 reflect the minimum required plus the fully phased-in capital conservation buffer of 2.50%; ratios for December 31, 2018 reflect the minimum required plus capital conservation buffer phase-in for 2018 of 1.875%.