Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 60,786	$ 65,679
Gross Unrealized Gains	837	16
Gross Unrealized Losses	0	(1,761)
Fair Value	61,623	63,934
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,217,638	733,279
Gross Unrealized Gains	30,955	1,487
Gross Unrealized Losses	(1,260)	(13,397)
Fair Value	1,247,333	721,369
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,949	99,926
Gross Unrealized Gains	84	0
Gross Unrealized Losses	0	(1,428)
Fair Value	10,033	98,498
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,468	12,506
Gross Unrealized Gains	167	16
Gross Unrealized Losses	0	(114)
Fair Value	12,635	12,408
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	164,263	26,566
Gross Unrealized Gains	6,298	327
Gross Unrealized Losses	(248)	(83)
Fair Value	170,313	26,810
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	48,318	53,173
Gross Unrealized Gains	670	0
Gross Unrealized Losses	0	(1,647)
Fair Value	48,988	51,526
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	917,102	596,825
Gross Unrealized Gains	18,021	1,160
Gross Unrealized Losses	(1,012)	(11,849)
Fair Value	934,111	586,136
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,969	9,962
Gross Unrealized Gains	278	0
Gross Unrealized Losses	0	(37)
Fair Value	10,247	$ 9,925
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	116,355
Gross Unrealized Gains	6,274
Gross Unrealized Losses	0
Fair Value	$ 122,629