Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Amortized Cost
Due in one year or less	$ 54,727
Due from one year to five years	28,720
Due from five years to ten years	95,658
Due after ten years	445,532
Amortized cost, before securities without debt maturities	624,637
Amortized cost basis	2,582,024
Estimated Fair Value
Due in one year or less	55,027
Due from one year to five years	29,342
Due from five years to ten years	96,933
Due after ten years	417,138
Available for sale securities, debt maturities, before securities without single maturities	598,440
Estimated Fair Value	2,534,701
Collateralized mortgage obligations
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	604,095
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	593,860
Mortgage-backed securities
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	1,353,292
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	$ 1,342,401