Stock Based Compensation Plan Stock-based Compensation Plan (Details 1) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		501,622	1,129,805	673,900
Equity Instruments Other than Options, Nonvested, Number		1,211,951	1,108,505	1,216,524	1,698,281
Shares vesting		$ 40.26	$ 28.53	$ 24.84
Granted		$ 46.18	$ 40.37	$ 29.06
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted		490,652	711,633	9,666
Restricted stock awarded and earned stock compensation, net of shares forfeited		$ 21,147	$ 30,671	$ 417
Equity Instruments Other than Options, Nonvested, Number		1,211,951
Shares vesting		$ 46.18	$ 40.21	$ 35.26
Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms		2 years 1 month 20 days	1 year 2 months 20 days	1 year 1 month 20 days
Outstanding at Year-End [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting		$ 42.59
Granted	[1]	$ 52,235,000
Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms		1 year 6 months 20 days

[1] Determined using the $43.10 closing price of PacWest common stock on December 31, 2015.