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Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Statement [Line Items]    
Available-for-sale securities, amortized cost basis $ 2,594,255 $ 2,494,059
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 24,807 28,740
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (59,835) (38,026)
Available-for-sale Securities 2,559,227 2,484,773
U.S. Government sponsored agency securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 132 25,154
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 2 35
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments 0 (53)
Available-for-sale Securities 134 25,136
State and municipal securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 405,274 256,746
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 2,043 6,019
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (15,676) 0
Available-for-sale Securities 391,641 262,765
Corporate debt securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 112,016 100,336
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 1,978 2,695
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (4,585) (6,076)
Available-for-sale Securities 109,409 96,955
Collateralized mortgage obligations    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 604,095 835,439
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 1,943 3,042
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (12,178) (16,972)
Available-for-sale Securities 593,860 821,509
Mortgage-backed securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 1,353,292 1,154,935
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 6,546 10,104
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (17,437) (6,204)
Available-for-sale Securities 1,342,401 1,158,835
Auction rate securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 107,215 106,772
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 0 0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (9,959) (8,713)
Available-for-sale Securities 97,256 98,059
Debt securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 2,582,024 2,479,382
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 12,512 21,895
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments (59,835) (38,018)
Available-for-sale Securities 2,534,701 2,463,259
Equity securities    
Statement [Line Items]    
Available-for-sale securities, amortized cost basis 12,231 14,677
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments 12,295 6,845
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments 0 (8)
Available-for-sale Securities $ 24,526 $ 21,514