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Related Party Transactions (Details) - USD ($)	3 Months Ended
Related Party Transactions (Details) - USD ($)	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 16, 2017	Aug. 01, 2014	Mar. 16, 2012
Related Party Transaction [Line Items]
Securities purchased under agreements to resell	$ 0		$ 25,913,000
Securities sold under agreements to repurchase	5,933,000		17,881,000
Preferred stock	229,475,000		229,475,000
Preferred stock dividends	3,864,000	$ 3,548,000
BSI \| Line of Credit \| BBVA Compass Bancshares, Inc.
Related Party Transaction [Line Items]
Due from related parties					$ 150,000,000
BSI \| Revolving Credit Facility \| Line of Credit \| BBVA Compass Bancshares, Inc.
Related Party Transaction [Line Items]
Due from related parties	0		0	$ 450,000,000		$ 420,000,000
BBVA
Related Party Transaction [Line Items]
Securities purchased under agreements to resell	0		0
Securities sold under agreements to repurchase	0		17,881,000
BBVA \| BBVA Compass Bancshares, Inc.
Related Party Transaction [Line Items]
Revenue from related parties	12,100,000	6,000,000
Fees on agreements	7,300,000	5,800,000
Derivatives designated as hedging instrument \| BBVA
Related Party Transaction [Line Items]
Derivative, notional amount	4,700,000,000		4,800,000,000
Free-standing derivatives not designated as hedging instrument \| Free-standing derivative instruments – risk management and other purposes \| BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	31,895,000		7,777,000
Uncommitted Demand Facility \| BSI \| Revolving Credit Facility \| Line of Credit \| BBVA Compass Bancshares, Inc.
Related Party Transaction [Line Items]
Due from related parties				$ 1,000,000,000
Revolving Note And Cash Subordinated Agreement \| BSI \| BBVA Compass Bancshares, Inc.
Related Party Transaction [Line Items]
Interest expense	120,000	367,000
Preferred Stock \| Series A Preferred Stock \| BBVA
Related Party Transaction [Line Items]
Preferred stock	229,000,000
Preferred stock dividends	3,900,000	$ 3,500,000
Cash flow hedges \| Derivatives designated as hedging instrument \| BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	74,000		(144,000)
Fair value hedges \| BBVA
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	$ (34,008,000)		$ (15,991,000)