Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Mortgage-backed securities
Investment securities
Fair value, less than twelve months	$ 1,168	$ 3,023
Gross unrealized losses, less than twelve months	(9)	(75)
Fair value, twelve months or greater	4,612	2,930
Gross unrealized losses, twelve months or greater	(140)	(165)
Fair value, total	5,780	5,953
Gross unrealized losses, total	(149)	(240)
State and political securities
Investment securities
Fair value, less than twelve months	2,409	14,819
Gross unrealized losses, less than twelve months	(1)	(128)
Fair value, twelve months or greater	6,559	13,648
Gross unrealized losses, twelve months or greater	(129)	(298)
Fair value, total	8,968	28,467
Gross unrealized losses, total	(130)	(426)
Other debt securities
Investment securities
Fair value, less than twelve months	5,765	10,133
Gross unrealized losses, less than twelve months	(14)	(153)
Fair value, twelve months or greater	36,588	34,776
Gross unrealized losses, twelve months or greater	(1,168)	(1,537)
Fair value, total	42,353	44,909
Gross unrealized losses, total	(1,182)	(1,690)
Debt securities
Investment securities
Fair value, less than twelve months	9,342	27,975
Gross unrealized losses, less than twelve months	(24)	(356)
Fair value, twelve months or greater	47,759	51,354
Gross unrealized losses, twelve months or greater	(1,437)	(2,000)
Fair value, total	57,101	79,329
Gross unrealized losses, total	$ (1,461)	$ (2,356)