Gold Lease Transactions - Additional Information (Detail) ¥ in Thousands, $ in Millions					1 Months Ended		3 Months Ended					9 Months Ended		12 Months Ended		28 Months Ended
	Apr. 10, 2015 USD ($) kg	Apr. 10, 2015 CNY (¥)	Mar. 05, 2015 USD ($) kg	Mar. 05, 2015 CNY (¥)	Aug. 28, 2013	Jan. 31, 2013	Sep. 30, 2015 USD ($)	Sep. 30, 2015 CNY (¥)	Mar. 31, 2015 USD ($) kg	Mar. 31, 2015 CNY (¥) kg	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) kg	Dec. 31, 2014 CNY (¥)	Apr. 30, 2015	Sep. 30, 2015 CNY (¥)	Sep. 30, 2015 kg	Sep. 30, 2015 lb	Apr. 10, 2015 CNY (¥) kg	Mar. 05, 2015 CNY (¥) kg	Dec. 31, 2014 CNY (¥) kg
Gold Lease Transactions [Line Items]
Proceeds from secured lines of credit | $												$ 121.2		$ 125.8
Interest expense, debt | $							$ 1.9				$ 1.8	5.6	$ 5.2
Gold Lease Outstanding														3,080				3,217				3,080
China Construction Bank
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period						6.00%
Gold Lease Outstanding																		1,515
Operating Leased Asset Residual Value | $							58.0					58.0
Shanghai Pudong Development Bank Ltd
Gold Lease Transactions [Line Items]
Cash deposit | $							20.6					20.6
Gold Lease Outstanding																		720	1,202
Operating Leased Asset Residual Value | $							45.0					45.0
Operating Leased Asset Value							$ 26.5					$ 26.5					¥ 168,200
Lessee Leasing Arrangements, Operating Leases, Term of Contract												1 year
Shanghai Pudong Development Bank Ltd | Maximum [Member]
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period																7.50%
Operating Lease Interest Rate							6.00%	6.00%
Shanghai Pudong Development Bank Ltd | Minimum [Member]
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period																3.20%
Operating Lease Interest Rate							2.80%	2.80%
CITIC Bank
Gold Lease Transactions [Line Items]
Cash deposit | $							$ 1.4					$ 1.4
Operating Leased Asset Residual Value | $							$ 19.0					$ 19.0
CITIC Bank | Maximum [Member]
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period			6.00%	6.00%	6.00%
CITIC Bank | Minimum [Member]
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period					5.60%
Gold lease transactions [Member]
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period							6.00%	6.00%	6.00%	6.00%
Proceeds from secured lines of credit			$ 6.0				$ 19.6	¥ 124,600	$ 35.2	¥ 218,200				$ 54.8
Cash deposit | $			$ 1.3
Gold Lease Outstanding									880	880								500
Deposits Returned Amount | $														27.6
Gold lease transactions [Member] | Shanghai Pudong Development Bank Ltd
Gold Lease Transactions [Line Items]
Line of credit facility, interest rate during period	3.20%	3.20%
Proceeds from secured lines of credit	$ 7.7	¥ 46,980												104.9	¥ 644,900
Cash deposit	$ 8.0													$ 66.8						¥ 50,000		¥ 410,300
Gold Lease Outstanding	197													2,380						197		2,380
Gold Lease Outstanding Returned														1,465								1,465
Gold lease transactions [Member] | Wuhan Bank
Gold Lease Transactions [Line Items]
Proceeds from secured lines of credit														$ 60.5	317,700
Gold Lease Outstanding														1,515								1,515
Deposits Returned Amount														$ 35.2								¥ 218,200
Gold Lease Outstanding Returned														880								880
Gold lease transactions [Member] | CITIC Bank
Gold Lease Transactions [Line Items]
Proceeds from secured lines of credit | ¥				¥ 36,800											¥ 336,600
Cash deposit | ¥																					¥ 8,000
Gold Lease Outstanding			150											1,300							150	1,300
Deposits Returned Amount | ¥																						¥ 169,700
Gold Lease Outstanding Returned														650								650