Stock-Based Compensation - Assumptions Used Estimate Fair Value of Employee Stock Purchase Plans (Detail) - $ / shares shares in Thousands	6 Months Ended					12 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares purchased for offering period	12,451	11,216	13,619	13,734	19,490
Fair value per share	$ 0.60	$ 0.43	$ 0.83	$ 0.30	$ 0.44
Assumptions
Risk-free interest rate (average)	0.11%	0.40%	0.80%	0.40%	0.11%	1.10%	1.20%	0.60%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Weighted average expected life (years)	6 months	6 months	6 months	6 months	6 months	4 years	4 years	4 years
Volatility (average)	103.80%	109.10%	74.00%	44.00%	45.00%	83.50%	82.90%	68.10%