Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 62,725	$ 65,679
Gross Unrealized Gains	411	16
Gross Unrealized Losses	(75)	(1,761)
Fair Value	63,061	63,934
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,202,341	733,279
Gross Unrealized Gains	22,556	1,487
Gross Unrealized Losses	(1,845)	(13,397)
Fair Value	1,223,052	721,369
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49,998	99,926
Gross Unrealized Gains	153	0
Gross Unrealized Losses	0	(1,428)
Fair Value	50,151	98,498
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,474	12,506
Gross Unrealized Gains	160	16
Gross Unrealized Losses	(1)	(114)
Fair Value	12,633	12,408
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	114,173	26,566
Gross Unrealized Gains	4,523	327
Gross Unrealized Losses	0	(83)
Fair Value	118,696	26,810
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	50,251	53,173
Gross Unrealized Gains	251	0
Gross Unrealized Losses	(74)	(1,647)
Fair Value	50,428	51,526
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	911,770	596,825
Gross Unrealized Gains	14,122	1,160
Gross Unrealized Losses	(1,845)	(11,849)
Fair Value	924,047	586,136
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,966	9,962
Gross Unrealized Gains	239	0
Gross Unrealized Losses	0	(37)
Fair Value	10,205	$ 9,925
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	116,434
Gross Unrealized Gains	3,519
Gross Unrealized Losses	0
Fair Value	$ 119,953