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, 2018	Dec. 31, 2017
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	$ 432,522	$ 196,051
Less than 12 Months, Gross Unrealized Losses	6,361	1,718
12 Months or Longer, Fair Value	255,149	103,991
12 Months or Longer, Gross Unrealized Losses	7,892	2,796
Total, Fair Value	687,671	300,042
Total, Gross Unrealized Losses	14,253	4,514
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	117,780	74,926
Less than 12 Months, Gross Unrealized Losses	1,245	652
12 Months or Longer, Fair Value	127,126	71,079
12 Months or Longer, Gross Unrealized Losses	3,496	1,431
Total, Fair Value	244,906	146,005
Total, Gross Unrealized Losses	4,741	2,083
Available-for-sale Securities and Held-to-maturity Securities [Abstract] (Deprecated 2018-01-31)
Less than 12 Months, Fair Value	550,302	270,977
Less than 12 Months, Gross Unrealized Losses	7,606	2,370
12 Months or Longer, Fair Value	382,275	175,070
12 Months or Longer, Gross Unrealized Losses	11,388	4,227
Total, Fair Value	932,577	446,047
Total, Gross Unrealized Losses	18,994	6,597
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
12 Months or Longer, Gross Unrealized Losses
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		9,988
Less than 12 Months, Gross Unrealized Losses		131
12 Months or Longer, Fair Value	22,073	12,196
12 Months or Longer, Gross Unrealized Losses	545	304
Total, Fair Value	22,073	22,184
Total, Gross Unrealized Losses	545	435
State and municipal
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	234,431	13,296
Less than 12 Months, Gross Unrealized Losses	3,958	198
12 Months or Longer, Fair Value	38,028	35,324
12 Months or Longer, Gross Unrealized Losses	1,896	893
Total, Fair Value	272,459	48,620
Total, Gross Unrealized Losses	5,854	1,091
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	14,952	2,430
Less than 12 Months, Gross Unrealized Losses	369	36
12 Months or Longer, Fair Value	16,786	15,805
12 Months or Longer, Gross Unrealized Losses	503	208
Total, Fair Value	31,738	18,235
Total, Gross Unrealized Losses	872	244
U.S. Government-sponsored mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	196,601	182,755
Less than 12 Months, Gross Unrealized Losses	2,400	1,520
12 Months or Longer, Fair Value	217,121	68,667
12 Months or Longer, Gross Unrealized Losses	5,996	1,903
Total, Fair Value	413,722	251,422
Total, Gross Unrealized Losses	8,396	3,423
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value	102,828	62,508
Less than 12 Months, Gross Unrealized Losses	876	485
12 Months or Longer, Fair Value	87,268	43,078
12 Months or Longer, Gross Unrealized Losses	2,447	919
Total, Fair Value	190,096	105,586
Total, Gross Unrealized Losses	3,323	$ 1,404
Foreign Investment
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position [Abstract]
Less than 12 Months, Fair Value
Less than 12 Months, Gross Unrealized Losses
12 Months or Longer, Fair Value	999
12 Months or Longer, Gross Unrealized Losses	1
Total, Fair Value	999
Total, Gross Unrealized Losses	$ 1