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Investments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Jan. 01, 2018
Schedule of Investments [Line Items]
Restricted certificate of deposit held		$ 25.6
Restricted certificate of deposit held, maturity date		Jan. 08, 2020
Transfer to investments	$ 3.4
Carrying value		$ 3.4
Other Receivables [Member]
Schedule of Investments [Line Items]
Note receivable		$ 0.9	$ 4.3
ASU 2016-01 [Member]
Schedule of Investments [Line Items]
Reclassification of net unrealized gains of marketable equity securities from AOCI to retained earnings				$ 3.2
Alabama State Industrial Development Authority [Member]
Schedule of Investments [Line Items]
Maturity date of bond		Jan. 01, 2020
Percentage of interest on bond		2.00%
Alabama State Industrial Development Authority [Member] | Taxable Revenue Bond [Member]
Schedule of Investments [Line Items]
Collateral deposit against outstanding principal amount		$ 25.6	25.6
Alabama State Industrial Development Authority [Member] | Taxable Revenue Bond [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Investments [Line Items]
Estimated fair value of bond		$ 25.6	$ 25.4
Investment [Member] | Issuer Concentration [Member] | Market Value of Total Investment Portfolio [Member]
Schedule of Investments [Line Items]
Investment concentration risk percentage		5.00%

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