Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Amortized Cost
Due in one year or less	$ 75,458
Due from one year to five years	85,840
Due from five years to ten years	124,190
Due after ten years	203,520
Amortized cost, before securities without debt maturities	489,008
Amortized cost basis	2,479,382
Estimated Fair Value
Due in one year or less	75,945
Due from one year to five years	87,877
Due from five years to ten years	127,103
Due after ten years	191,990
Available for sale securities, debt maturities, before securities without single maturities	482,915
Estimated Fair Value	2,463,259
Collateralized mortgage obligations
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	835,439
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	821,509
Mortgage-backed securities
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	1,154,935
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	$ 1,158,835