Merchandise Trusts - Additional Information (Detail) - Variable Interest Entity, Primary Beneficiary - Merchandise Trusts - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Trust assets, fair value	$ 494,596,000		$ 494,596,000		$ 464,676,000
Purchases of available for sale securities			47,100,000
Sales, maturities and paydowns of available for sale securities			28,100,000
Trust assets, cost	501,519,000		501,519,000		489,361,000
Other Than Temporarily Impaired Securities
Schedule of Available-for-sale Securities [Line Items]
Trust assets, fair value		$ 400,000		$ 400,000
Trust assets, cost		600,000		600,000
Other than temporary impairments loss	0	$ 0	0	$ 200,000
West Virginia Trust Receivable
Schedule of Available-for-sale Securities [Line Items]
Trust assets, fair value	8,332,000		8,332,000		8,175,000
Trust assets, cost	$ 8,332,000		$ 8,332,000		$ 8,175,000