Reconciliation of Merchandise Trust Activities (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Balance, beginning of period	$ 464,676
Balance, end of period	494,596
Variable Interest Entity, Primary Beneficiary | Merchandise Trusts
Schedule of Available-for-sale Securities [Line Items]
Balance, beginning of period	464,676	$ 484,820
Contributions	30,259	31,667
Distributions	(29,645)	(21,231)
Interest and dividends	11,686	8,391
Capital gain distributions	263	(741)
Realized gains and losses	2,337	14,453
Taxes	(1,694)	(3,026)
Fees	(1,048)	(1,632)
Unrealized change in fair value	17,762	(33,774)
Balance, end of period	$ 494,596	$ 478,927