Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) $ in Thousands	Jun. 30, 2016 USD ($)
Amortized Cost
Due in one year or less	$ 55,965
Due from one year to five years	44,833
Due from five years to ten years	94,787
Due after ten years	340,172
Amortized cost, before securities without debt maturities	535,757
Amortized Cost	2,479,877
Estimated Fair Value
Due in one year or less	56,628
Due from one year to five years	46,408
Due from five years to ten years	97,933
Due after ten years	333,957
Available for sale securities, debt maturities, before securities without single maturities	534,926
Estimated Fair Value	2,509,035
Collateralized Mortgage Obligations [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	701,853
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	706,346
Mortgage-Backed Securities [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	1,242,267
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	$ 1,267,763