Receivables - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables past due or deemed uncollectible	$ 34,865,000	$ 22,212,000
Interest-bearing financing fee receivables	80,536,000	76,133,000
Allowance for doubtful accounts receivables	23,746,000	16,386,000	$ 12,882,000	$ 23,540,000
Aggregate carrying amount of non-interest bearing receivables	491,080,000	562,149,000
Financing Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts receivables	$ 0	$ 0