Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 1,175
Due from one year to five years	34,996
Due from five years to ten years	355,584
Due after ten years	916,659
Amortized cost, before securities without debt maturities	1,308,414
Amortized Cost	2,735,991
Estimated Fair Value
Due in one year or less	1,175
Due from one year to five years	35,936
Due from five years to ten years	355,472
Due after ten years	922,645
Available for sale securities, debt maturities, before securities without single maturities	1,315,228
Estimated Fair Value	2,790,834	$ 2,497,537
Amortized Cost
Due in one year or less	0
Due from one year to five years	0
Due from five years to ten years	0
Due after ten years	0
Debt securities, held-to-maturity, maturity, allocated and single maturity date, amortized cost, total	0
Amortized Cost, Held to Maturity	350,606	369,841
Estimated Fair Value
Due in one year or less	0
Due from one year to five years	0
Due from five years to ten years	0
Due after ten years	0
Debt securities, held-to-maturity, maturity, Allocated and single maturity date, fair value	0
Estimated Fair Value, Held to Maturity	372,273
Collateralized Mortgage Obligations [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	638,458
Amortized Cost	638,458
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	667,652
Estimated Fair Value	667,652
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	0
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	0
Commercial Mortgage Backed Securities [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	574,860
Amortized Cost	574,860
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	587,325
Estimated Fair Value	587,325
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	0
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	0
Mortgage-Backed Securities [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	214,259
Amortized Cost	214,259
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	220,629
Estimated Fair Value	220,629
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	350,606
Amortized Cost, Held to Maturity	350,606	369,841
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	372,273
Estimated Fair Value, Held to Maturity	$ 372,273	$ 383,705