Loans - Loans Acquired (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Business Acquisition [Line Items]
Expected losses and foregone interest	$ (157,660)		$ (160,183)
Fair value of acquired loans at acquisition	14,500	$ 12,700
Non-accretable difference (expected losses and foregone interest)	(2,369)	$ (1,358)
Sabadell United
Business Acquisition [Line Items]
Loans acquired	4,026,240
Contractually required principal and interest at acquisition	4,914,185
Expected losses and foregone interest	(54,226)
Cash flows expected to be collected at acquisition	4,859,959
Fair value of acquired loans at acquisition	3,960,308
Contractually required principal and interest at acquisition	111,114
Non-accretable difference (expected losses and foregone interest)	(12,245)
Cash flows expected to be collected at acquisition	98,869
Accretable yield	(32,937)
Basis in acquired loans at acquisition	$ 65,932