Receivables - Additional Information (Detail) - USD ($)	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables past due or deemed uncollectible	$ 42,434,000		$ 34,865,000
Interest-bearing financing fee receivables	74,668,000		80,536,000
Allowance for doubtful accounts receivables	34,956,000	$ 38,557,000	23,746,000	$ 25,094,000	$ 29,662,000	$ 16,386,000
Aggregate carrying amount of non-interest bearing receivables	639,729,000		491,080,000
Financing Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts receivables	$ 0		$ 0