Investment Securities - Investments' Gross Unrealized Losses and Fair Value Aggregated by Investment Category and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	$ 203,946	$ 432,522
Less than 12 Months, Gross Unrealized Losses	2,133	6,361
12 Months or Longer, Fair Value	20,796	255,149
12 Months or Longer, Gross Unrealized Losses	78	7,892
Total, Fair Value	224,742	687,671
Total, Gross Unrealized Losses	2,211	14,253
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	150,216	117,780
Less than 12 Months, Gross Unrealized Losses	475	1,245
12 Months or Longer, Fair Value	20,458	127,126
12 Months or Longer, Gross Unrealized Losses	70	3,496
Total, Fair Value	170,674	244,906
Total, Gross Unrealized Losses	545	4,741
Less than 12 Months, Fair Value	354,162	550,302
Less than 12 Months, Gross Unrealized Losses	2,608	7,606
12 Months or Longer, Fair Value	41,254	382,275
12 Months or Longer, Gross Unrealized Losses	148	11,388
Total, Fair Value	395,416	932,577
Total, Gross Unrealized Losses	2,756	18,994
Government Agency and Municipal Bonds and Notes
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		1,490
Less than 12 Months, Gross Unrealized Losses		3
12 Months or Longer, Fair Value		0
12 Months or Longer, Gross Unrealized Losses		0
Total, Fair Value		1,490
Total, Gross Unrealized Losses		3
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	3,016	0
Less than 12 Months, Gross Unrealized Losses	4	0
12 Months or Longer, Fair Value	12,467	22,073
12 Months or Longer, Gross Unrealized Losses	33	545
Total, Fair Value	15,483	22,073
Total, Gross Unrealized Losses	37	545
State and municipal
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	76,273	234,431
Less than 12 Months, Gross Unrealized Losses	807	3,958
12 Months or Longer, Fair Value	0	38,028
12 Months or Longer, Gross Unrealized Losses	0	1,896
Total, Fair Value	76,273	272,459
Total, Gross Unrealized Losses	807	5,854
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	22,947	14,952
Less than 12 Months, Gross Unrealized Losses	107	369
12 Months or Longer, Fair Value	0	16,786
12 Months or Longer, Gross Unrealized Losses	0	503
Total, Fair Value	22,947	31,738
Total, Gross Unrealized Losses	107	872
U.S. Government-sponsored mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	127,673	196,601
Less than 12 Months, Gross Unrealized Losses	1,326	2,400
12 Months or Longer, Fair Value	20,796	217,121
12 Months or Longer, Gross Unrealized Losses	78	5,996
Total, Fair Value	148,469	413,722
Total, Gross Unrealized Losses	1,404	8,396
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	124,253	102,828
Less than 12 Months, Gross Unrealized Losses	364	876
12 Months or Longer, Fair Value	7,991	87,268
12 Months or Longer, Gross Unrealized Losses	37	2,447
Total, Fair Value	132,244	190,096
Total, Gross Unrealized Losses	$ 401	3,323
Foreign investment
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value		0
Less than 12 Months, Gross Unrealized Losses		0
12 Months or Longer, Fair Value		999
12 Months or Longer, Gross Unrealized Losses		1
Total, Fair Value		999
Total, Gross Unrealized Losses		$ 1