Derivative Financial Instruments - Significant Assumptions Utilized in Binomial Lattice Process (Detail) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Level 1 [Member]
Derivative [Line Items]
Linked common shares	1,725,000	1,800,000	1,725,000
Quoted market price on valuation date	$ 2.960	$ 3.725	$ 2.970
Contractual exercise rate	$ 2.4648	$ 2.5000	$ 2.4648
Term (years)	3 months 11 days	1 year 3 months 11 days	9 months 11 days
Level 2 [Member]
Derivative [Line Items]
Linked common shares	525,000	525,000	525,000
Quoted market price on valuation date	$ 2.960	$ 3.725	$ 2.970
Contractual exercise rate	$ 2.4648	$ 2.7500	$ 2.4648
Term (years)	9 months 15 days	1 year 9 months 15 days	1 year 3 months 11 days
Level 3 [Member]
Derivative [Line Items]
Linked common shares	1,562,500	1,562,500	1,562,500
Quoted market price on valuation date	$ 2.960	$ 3.725	$ 2.970
Contractual exercise rate	$ 3.60	$ 3.60	$ 3.60
Term (years)	3 years 10 months 10 days	4 years 10 months 10 days	4 years 4 months 6 days
Minimum [Member] | Level 1 [Member]
Derivative [Line Items]
Range of market volatilities	17.30%	48.70%	33.10%
Risk free rates using zero coupon US Treasury security rates	0.02%	0.04%	0.02%
Minimum [Member] | Level 2 [Member]
Derivative [Line Items]
Range of market volatilities	31.70%	48.90%	33.80%
Risk free rates using zero coupon US Treasury security rates	0.02%	0.04%	0.02%
Minimum [Member] | Level 3 [Member]
Derivative [Line Items]
Range of market volatilities	44.30%	48.80%	39.20%
Risk free rates using zero coupon US Treasury security rates	0.04%	0.09%	0.05%
Maximum [Member] | Level 1 [Member]
Derivative [Line Items]
Range of market volatilities	53.60%	73.10%	49.17%
Risk free rates using zero coupon US Treasury security rates	0.04%	0.27%	0.11%
Maximum [Member] | Level 2 [Member]
Derivative [Line Items]
Range of market volatilities	53.50%	72.20%	63.60%
Risk free rates using zero coupon US Treasury security rates	0.10%	0.27%	0.16%
Maximum [Member] | Level 3 [Member]
Derivative [Line Items]
Range of market volatilities	62.30%	72.50%	70.20%
Risk free rates using zero coupon US Treasury security rates	0.66%	0.72%	0.54%