Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Equity securities:
Carrying Value	$ 6,800	$ 6,700
Held to maturity
Equity and Debt Securities, Amortized Cost	208,779	211,960
Equity and Debt Securities, Gross Unrealized Gain (Loss)	2,251	(2,415)
Equity and Debt Securities, Marketable Securities	211,030	209,545
Investment funds - debt securities [Member]
Equity securities:
Amortized Cost/Cost	21,083	31,934
Gross Unrealized Gain (Loss)	45	(568)
Carrying Value	21,128	31,366
Investment funds - U.S. treasuries [Member]
Available for sale
Amortized Cost/Cost	9,022	8,983
Gross Unrealized Gain (Loss)	(25)	(31)
Carrying Value	8,997	8,952
Common stock and stock funds [Member]
Equity securities:
Amortized Cost/Cost	41,997	39,731
Gross Unrealized Gain (Loss)	2,226	(1,671)
Carrying Value	44,223	38,060
Investment-grade unsecured bonds [Member]
Available for sale
Amortized Cost/Cost	4,152	4,125
Gross Unrealized Gain (Loss)	5	(145)
Carrying Value	4,157	3,980
Mortgage backed securities [Member]
Held to maturity
Amortized Cost/Cost	132,525	127,187
Gross Unrealized Gain (Loss)	0	0
Carrying Value	$ 132,525	$ 127,187

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