Organization (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) acquisition bank_branch	Dec. 31, 2015 USD ($)
General Introduction [Abstract]
Assets	$ 21,031,009	$ 21,288,490
Gross loans and leases	14,500,000
Total deposits	15,441,375	15,666,182
Total stockholders' equity	$ 4,456,592	4,397,691
Number of businesses acquired | acquisition	28
Outstanding lease balance disposed	$ (139,000)
Accumulated Deficit
General Introduction [Abstract]
Total stockholders' equity	$ 104,363	$ 13,907
CapitalSource Inc.
General Introduction [Abstract]
Business Acquisition, Effective Date of Acquisition		Apr. 07, 2014
NORTH CAROLINA
General Introduction [Abstract]
Retail Branch Locations | bank_branch	1
CALIFORNIA
General Introduction [Abstract]
Retail Branch Locations | bank_branch	79