Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill	$ 1,720,479	$ 1,720,479	$ 208,743	$ 79,866
Goodwill, Impairment Loss			(6,645)
Goodwill		2,176,291	1,720,479	208,743
American Perspective Bank [Member]
Goodwill [Roll Forward]
Goodwill, Other Changes				(193)
First California Financial Group, Inc. [Member]
Goodwill [Roll Forward]
Goodwill, Acquired During Period				$ 129,070
Square 1 Financial, Inc. [Member]
Goodwill [Roll Forward]
Goodwill, Acquired During Period		447,911
CapitalSource Inc. [Member]
Goodwill [Line Items]
Goodwill, Subsequent Recognition of Deferred Tax Asset	$ 7,900	$ 7,901
Goodwill [Roll Forward]
Goodwill, Acquired During Period			$ 1,518,381