Loans, Allowance for Loan and Lease Losses, and Reserve for Off-Balance Sheet Credit Commitments (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts notes and loans receivable
Loans and leases, excluding covered loans	$ 20,337,206,000	$ 17,170,438,000
Less: Allowance for loan and lease losses	(310,149,000)	(302,584,000)	(277,888,000)
Loans and leases, excluding covered loans, net	20,027,057,000	16,867,854,000
Covered loans	510,979,000	716,911,000
Less: Allowance for loan losses	(8,608,000)	(15,922,000)	(44,781,000)
Covered loans, net	502,371,000	700,989,000
Total loans and leases	20,848,185,000	17,887,349,000
Net loans and leases	20,529,428,000	17,568,843,000
FDIC indemnification asset	50,511,000	89,227,000
FDIC clawback liability	15,106,000
Net deferred costs (fees)	200,000	(2,300,000)
Aggregate amount of loans to executive officers, directors and companies and individuals affiliated with or guaranteed by officers and directors of the Company and the Bank	63,800,000	122,400,000
New loans and advances made	82,300,000
Repayments of loans and advances	77,200,000
Interest income recognized on loans to executive officers, directors and companies and individuals affiliated with or guaranteed by officers and directors of the Company and the Bank	1,800,000	3,400,000	2,200,000
Past due and nonaccrual loans	0
Imperial Capital Bank
Accounts notes and loans receivable
Covered loans	456,177,000	630,754,000
FDIC indemnification asset	43,517,000
1st Pacific Bank
Accounts notes and loans receivable
Covered loans	23,895,000	40,110,000
FDIC indemnification asset	2,125,000
FDIC clawback liability	12,566,000
Sun West Bank
Accounts notes and loans receivable
Covered loans	9,353,000	18,761,000
FDIC indemnification asset	1,817,000
FDIC clawback liability	2,355,000
Nevada Commerce Bank
Accounts notes and loans receivable
Covered loans	21,554,000	27,286,000
FDIC indemnification asset	3,052,000
FDIC clawback liability	185,000
Commercial
Accounts notes and loans receivable
Loans and leases, excluding covered loans	9,360,976,000	7,562,300,000
Covered loans	1,969,000	10,009,000
Commercial | Loans previously reported as lease financing
Accounts notes and loans receivable
Loans and leases, excluding covered loans		158,200,000
Commercial | Imperial Capital Bank
Accounts notes and loans receivable
Sharing of recoveries with FDIC on expiration date (as a percent)	80.00%
Sharing of recoveries with FDIC on termination date (as a percent)	80.00%
Commercial | 1st Pacific Bank
Accounts notes and loans receivable
Sharing of recoveries with FDIC on expiration date (as a percent)	80.00%
Sharing of recoveries with FDIC on termination date (as a percent)	80.00%
Commercial | Sun West Bank
Accounts notes and loans receivable
Sharing of recoveries with FDIC on expiration date (as a percent)	80.00%
Sharing of recoveries with FDIC on termination date (as a percent)	80.00%
Commercial | Nevada Commerce Bank
Accounts notes and loans receivable
Sharing of recoveries with FDIC on expiration date (as a percent)	80.00%
Sharing of recoveries with FDIC on termination date (as a percent)	80.00%
Commercial real estate mortgages
Accounts notes and loans receivable
Loans and leases, excluding covered loans	3,539,703,000	3,223,001,000
Less: Allowance for loan and lease losses	(44,745,000)	(50,678,000)	(48,901,000)
Covered loans	481,689,000	666,628,000
Residential mortgages
Accounts notes and loans receivable
Loans and leases, excluding covered loans	5,106,803,000	4,554,311,000
Less: Allowance for loan and lease losses	(10,296,000)	(11,540,000)	(10,558,000)
Covered loans	4,455,000	4,976,000
Real estate construction
Accounts notes and loans receivable
Loans and leases, excluding covered loans	710,224,000	367,004,000
Less: Allowance for loan and lease losses	(9,115,000)	(6,351,000)	(11,784,000)
Covered loans	18,790,000	31,184,000
Home equity loans and lines of credit
Accounts notes and loans receivable
Loans and leases, excluding covered loans	785,796,000	709,344,000
Less: Allowance for loan and lease losses	(6,609,000)	(6,677,000)	(7,283,000)
Covered loans	3,820,000	3,695,000
Installment
Accounts notes and loans receivable
Loans and leases, excluding covered loans	184,613,000	151,955,000
Less: Allowance for loan and lease losses	(2,228,000)	(1,842,000)	(1,858,000)
Covered loans	256,000	419,000
Lease financing
Accounts notes and loans receivable
Loans and leases, excluding covered loans	649,091,000	602,523,000
Lease financing | Loans previously reported as lease financing
Accounts notes and loans receivable
Loans and leases, excluding covered loans		$ (158,200,000)