Investment Securities Schedule of Amortized Cost and Fair Values of Debt Securities by Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Due in one year or less	$ 12,731
Due from one year to five years	31,144
Due from five years to ten years	301,186
Due after ten years	927,473
Amortized cost, before securities without debt maturities	1,272,534
Amortized Cost	2,548,261
Estimated Fair Value
Due in one year or less	12,731
Due from one year to five years	32,687
Due from five years to ten years	313,583
Due after ten years	960,893
Available for sale securities, debt maturities, before securities without single maturities	1,319,894
Estimated Fair Value	2,644,299	$ 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	330,514	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	354,109
Collateralized Mortgage Obligations [Member]
Amortized Cost
Available-for-sale securities, amortized cost without single maturity date	559,281
Amortized Cost	559,281
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	578,394
Estimated Fair Value	578,394
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	560,294
Amortized Cost	560,294
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	585,143
Estimated Fair Value	585,143
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	156,152
Amortized Cost	156,152
Estimated Fair Value
Available-for-sale securities, debt maturities, without single maturity date, fair value	160,868
Estimated Fair Value	160,868
Amortized Cost
Debt securities, held-to-maturity, maturity, without single maturity date, amortized cost	330,514
Amortized Cost, Held to Maturity	330,514	369,841
Estimated Fair Value
Debt securities, held-to-maturity, maturity, without single maturity date, fair value	354,109
Estimated Fair Value, Held to Maturity	$ 354,109	$ 383,705