Related Party Transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 01, 2014	Mar. 16, 2012
Related Party Transaction [Line Items]
Securities purchased under agreements to resell	$ 279,106,000	$ 566,539,000
Securities sold under agreements to repurchase	76,609,000	435,684,000
FHLB and other borrowings	5,438,620,000	4,809,843,000
BBVA
Related Party Transaction [Line Items]
Securities purchased under agreements to resell	26,404,000	97,970,000
Securities sold under agreements to repurchase	74,049,000	435,684,000
Fair value hedges | BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	(9,405,000)	0
Cash flow hedges | BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	0	1,693,000
Free-standing derivative instruments – risk management and other purposes | BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	(20,082,000)	9,512,000
BBVA | BBVA
Related Party Transaction [Line Items]
Related party, income	21,700,000	13,200,000	$ 8,800,000
Related party, expenses	25,400,000	26,800,000	20,300,000
BBVA | Line of credit | BSI
Related Party Transaction [Line Items]
Due from related parties	150,000,000			$ 150,000,000
BBVA | Line of credit | Revolving credit facility | BSI
Related Party Transaction [Line Items]
Due from related parties					$ 420,000,000
Revolving Note And Cash Subordinated Agreement | BBVA | BSI
Related Party Transaction [Line Items]
FHLB and other borrowings	0	0
Related party, interest expense	2,300,000	138,000	29,000
Related party, expenses	250,000	313,000	$ 0
Derivatives designated as hedging instrument | BBVA
Related Party Transaction [Line Items]
Derivative notional amount	$ 5,300,000,000	$ 4,400,000,000