Capital Stock - Summary of Company's Restricted Shares Issued and Subject to Repurchase (Detail) (Restricted shares subject to repurchase [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted shares subject to repurchase [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Stock Awards Outstanding, Beginning balance	1,456,987	1,156,078
Shares issued subject to vesting during the period	500,894	686,273	1,156,078
Shares vested during the period	(614,117)	(385,364)
Number of Restricted Stock Awards Outstanding, Ending balance	1,343,764	1,456,987	1,156,078