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Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Statement [Line Items]    
Available-for-sale securities, amortized cost basis $ 2,494,059 $ 2,312,087
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 28,740 49,212
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (38,026) (37,928)
Available-for-sale Securities 2,484,773 2,323,371
U.S. Government securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 0 200
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 0 0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments 0 0
Available-for-sale Securities 0 200
U.S. Government sponsored agency securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 25,154 209
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 35 5
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (53) 0
Available-for-sale Securities 25,136 214
State and municipal securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 256,746 238,250
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 6,019 7,231
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments 0 (266)
Available-for-sale Securities 262,765 245,215
Corporate debt securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 100,336 99,016
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 2,695 5,126
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (6,076) (6,108)
Available-for-sale Securities 96,955 98,034
Collateralized mortgage obligations    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 835,439 917,395
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 3,042 5,705
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (16,972) (20,787)
Available-for-sale Securities 821,509 902,313
Mortgage-backed securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 1,154,935 914,797
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 10,104 16,978
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (6,204) (2,944)
Available-for-sale Securities 1,158,835 928,831
Auction rate securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 106,772 108,751
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 0 0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (8,713) (7,810)
Available-for-sale Securities 98,059 100,941
Debt securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 2,479,382 2,278,618
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 21,895 35,045
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (38,018) (37,915)
Available-for-sale Securities 2,463,259 2,275,748
Equity securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 14,677 33,469
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 6,845 14,167
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (8) (13)
Available-for-sale Securities $ 21,514 $ 47,623