Investments - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 255,984	$ 110,081
Less than 12 months, unrealized losses	1,319	(2,548)
12 months or more, fair value	41,491	492,727
12 months or more, unrealized losses	435	(12,610)
Total, fair value	297,475	602,808
Total, unrealized losses	1,754	(15,158)
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value		19,622
Less than 12 months, unrealized losses		322
12 months or more, fair value		78,876
12 months or more, unrealized losses		1,106
Total, fair value		98,498
Total, unrealized losses		1,428
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	56,327	3,102
Less than 12 months, unrealized losses	363	15
12 months or more, fair value	0	14,156
12 months or more, unrealized losses	0	182
Total, fair value	56,327	17,258
Total, unrealized losses	363	197
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	131,693	87,357
Less than 12 months, unrealized losses	756	2,211
12 months or more, fair value	41,491	389,770
12 months or more, unrealized losses	435	11,285
Total, fair value	173,184	477,127
Total, unrealized losses	1,191	13,496
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	67,964
Less than 12 months, unrealized losses	200
12 months or more, fair value	0
12 months or more, unrealized losses	0
Total, fair value	67,964
Total, unrealized losses	$ 200
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value		0
Less than 12 months, unrealized losses		0
12 months or more, fair value		9,925
12 months or more, unrealized losses		37
Total, fair value		9,925
Total, unrealized losses		$ 37