Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	$ 0
Held-to-maturity, less than 12 months, gross unrealized losses	0
Held-to-maturity, 12 months or more, estimated fair value	8,139
Held-to-maturity, 12 months or more, gross unrealized losses	(71)
Held-to-maturity, total, estimated fair value	8,139
Held-to-maturity, total, gross unrealized losses	(71)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	49,038
Available-for-sale, less than 12 months, gross unrealized losses	(210)
Available-for-sale, 12 months or more, estimated fair value	893,079
Available-for-sale, 12 months or more, gross unrealized losses	(8,583)
Available-for-sale, total, estimated fair value	942,117
Available-for-sale, total, gross unrealized losses	(8,793)
U.S. Government agencies
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	0
Held-to-maturity, less than 12 months, gross unrealized losses	0
Held-to-maturity, 12 months or more, estimated fair value	0
Held-to-maturity, 12 months or more, gross unrealized losses	0
Held-to-maturity, total, estimated fair value	0
Held-to-maturity, total, gross unrealized losses	0
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	0
Available-for-sale, less than 12 months, gross unrealized losses	0
Available-for-sale, 12 months or more, estimated fair value	114,443
Available-for-sale, 12 months or more, gross unrealized losses	(1,380)
Available-for-sale, total, estimated fair value	114,443
Available-for-sale, total, gross unrealized losses	(1,380)
Mortgage-backed securities
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	0
Held-to-maturity, less than 12 months, gross unrealized losses	0
Held-to-maturity, 12 months or more, estimated fair value	5,845
Held-to-maturity, 12 months or more, gross unrealized losses	(59)
Held-to-maturity, total, estimated fair value	5,845
Held-to-maturity, total, gross unrealized losses	(59)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	20,839
Available-for-sale, less than 12 months, gross unrealized losses	(102)
Available-for-sale, 12 months or more, estimated fair value	749,380
Available-for-sale, 12 months or more, gross unrealized losses	(6,948)
Available-for-sale, total, estimated fair value	770,219
Available-for-sale, total, gross unrealized losses	(7,050)
State and political subdivisions
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	0
Held-to-maturity, less than 12 months, gross unrealized losses	0
Held-to-maturity, 12 months or more, estimated fair value	2,294
Held-to-maturity, 12 months or more, gross unrealized losses	(12)
Held-to-maturity, total, estimated fair value	2,294
Held-to-maturity, total, gross unrealized losses	(12)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	23,205
Available-for-sale, less than 12 months, gross unrealized losses	(15)
Available-for-sale, 12 months or more, estimated fair value	29,156
Available-for-sale, 12 months or more, gross unrealized losses	(255)
Available-for-sale, total, estimated fair value	52,361
Available-for-sale, total, gross unrealized losses	(270)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	4,994
Available-for-sale, less than 12 months, gross unrealized losses	(93)
Available-for-sale, 12 months or more, estimated fair value	100
Available-for-sale, 12 months or more, gross unrealized losses	0
Available-for-sale, total, estimated fair value	5,094
Available-for-sale, total, gross unrealized losses	$ (93)