Stock Based Compensation Plan Stock-based Compensation Plan (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	1,129,805		673,900	226,400
Equity Instruments Other than Options, Nonvested, Number	1,108,505		1,216,524	1,698,281	1,675,730
Shares issued by the Company upon vesting	$ 28.53		$ 24.84	$ 21.69
Granted	$ 40.37		$ 29.06	$ 23.77
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	1,081,505		27,000
Restricted stock awarded and earned stock compensation, net of shares forfeited	$ 49,165		$ 1,228
Equity Instruments Other than Options, Nonvested, Number	1,108,505
Shares issued by the Company upon vesting	$ 40.37		$ 35.08
Granted	$ 50,393,000.00	[1]
Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	1 year 6 months 37 days		1 year 6 months 37 days

[1] (1)Determined using the $45.46 closing price of PacWest common stock on December 31, 2014.