Master Netting and Similar Agreements—Repurchase, Reverse Repurchase, and Securities Borrowing Transactions (Schedule of the Remaining Contractual Maturity by Collateral Type of Securities Sold Under Agreements To Repurchase) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	$ 713,152	$ 656,602
Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	703,200	647,571
Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	9,952	9,031
U.S. treasuries
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	24,153	13,830
U.S. treasuries | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	24,153	13,830
U.S. treasuries | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	0	0
Government agency issued MBS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	390,764	430,186
Government agency issued MBS | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	383,835	424,821
Government agency issued MBS | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	6,929	5,365
Government agency issued CMO
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	57,553	57,703
Government agency issued CMO | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	54,530	54,037
Government agency issued CMO | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	3,023	3,666
Government guaranteed loans (SBA and USDA)
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	240,682	154,883
Government guaranteed loans (SBA and USDA) | Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	240,682	154,883
Government guaranteed loans (SBA and USDA) | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total Securities sold under agreements to repurchase	$ 0	$ 0