Investment Securities (Unrealized Position - Less than 12 Mos., 12 Mos. or Longer) (Details 4) $ in Thousands	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 465,117	$ 261,265
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,189	1,264
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	474,384	1,045,677
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	7,587	22,177
Debt Securities, Available-for-sale, Unrealized Loss Position	939,501	1,306,942
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	9,776	23,441
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	443,459	131,631
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,365)	(343)
12 Months or Longer, Fair Value	514,291	2,484,212
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(8,037)	(79,714)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(9,402)	(80,057)
Less than 12 Months, Gross Unrealized Losses	(1,365)	(343)
12 Months or Longer, Gross Unrealized Losses	(8,037)	(79,714)
Total, Fair Value	$ 957,750	2,615,843
Number of Investment Securities in Unrealized Loss Position | security	254
Debt Securities Issued by the U.S. Treasury and Government Agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 65,479	157,058
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	188	964
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	101,761	173,763
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,259	1,613
Debt Securities, Available-for-sale, Unrealized Loss Position	167,240	330,821
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1,447	2,577
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	0	99,440
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	(237)
12 Months or Longer, Fair Value	39,984	134,239
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(31)	(856)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(31)	(1,093)
Less than 12 Months, Gross Unrealized Losses	0	(237)
12 Months or Longer, Gross Unrealized Losses	(31)	(856)
Total, Fair Value	39,984	233,679
Debt Securities Issued by States and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	6,788	38,138
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	59
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	440	156,772
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	972
Debt Securities, Available-for-sale, Unrealized Loss Position	7,228	194,910
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	14	1,031
Debt Securities Issued by Corporations
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	25,892	59,770
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	326	231
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	74,693	163,371
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	307	1,626
Debt Securities, Available-for-sale, Unrealized Loss Position	100,585	223,141
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	633	1,857
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	4,416	0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(15)	0
12 Months or Longer, Fair Value	10,421	95,511
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(123)	(1,755)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(138)	(1,755)
Less than 12 Months, Gross Unrealized Losses	(15)	0
12 Months or Longer, Gross Unrealized Losses	(123)	(1,755)
Total, Fair Value	14,837	95,511
Mortgage-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	366,958	6,299
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,661	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	297,490	551,771
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,021	17,966
Debt Securities, Available-for-sale, Unrealized Loss Position	664,448	558,070
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	7,682	17,976
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	439,043	32,191
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,350)	(106)
12 Months or Longer, Fair Value	463,886	2,254,462
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(7,883)	(77,103)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(9,233)	(77,209)
Less than 12 Months, Gross Unrealized Losses	(1,350)	(106)
12 Months or Longer, Gross Unrealized Losses	(7,883)	(77,103)
Total, Fair Value	902,929	2,286,653
Residential - Government Agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	119,271	6,299
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	526	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	170,805	19,011
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,741	919
Debt Securities, Available-for-sale, Unrealized Loss Position	290,076	25,310
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3,267	929
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	88,061	12,974
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(422)	(45)
12 Months or Longer, Fair Value	255,816	1,491,747
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4,926)	(51,728)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(5,348)	(51,773)
Less than 12 Months, Gross Unrealized Losses	(422)	(45)
12 Months or Longer, Gross Unrealized Losses	(4,926)	(51,728)
Total, Fair Value	343,877	1,504,721
Residential - U.S. Government Sponsored Enterprises
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	187,861	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	816	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	73,720	473,380
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,058	12,563
Debt Securities, Available-for-sale, Unrealized Loss Position	261,581	473,380
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1,874	12,563
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	340,453	0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(909)	0
12 Months or Longer, Fair Value	156,018	617,000
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,569)	(20,259)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(2,478)	(20,259)
Less than 12 Months, Gross Unrealized Losses	(909)	0
12 Months or Longer, Gross Unrealized Losses	(1,569)	(20,259)
Total, Fair Value	496,471	617,000
Commercial - Government Agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	59,826	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	319	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	52,965	59,380
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,222	4,484
Debt Securities, Available-for-sale, Unrealized Loss Position	112,791	59,380
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	2,541	4,484
Held-to-Maturity Securities, Continuous Unrealized Loss Position [Abstract]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	10,529	19,217
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)	(61)
12 Months or Longer, Fair Value	52,052	145,715
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,388)	(5,116)
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	(1,407)	(5,177)
Less than 12 Months, Gross Unrealized Losses	(19)	(61)
12 Months or Longer, Gross Unrealized Losses	(1,388)	(5,116)
Total, Fair Value	$ 62,581	$ 164,932