Stockholder's Equity - Additional Information (Detail)									12 Months Ended
	May. 29, 2015 USD ($) agreement $ / shares shares	Dec. 23, 2014 USD ($) shares	Sep. 17, 2014 USD ($) $ / shares shares	Feb. 11, 2014 USD ($) $ / shares shares	Feb. 05, 2014 shares	Aug. 16, 2013 shares	Aug. 13, 2013 USD ($) $ / shares shares	Sep. 02, 2011 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares	Sep. 08, 2015 $ / shares shares	Sep. 07, 2015 shares	Sep. 11, 2014 USD ($) $ / shares
Stockholders Equity [Line Items]
Number of Investment Agreements | agreement	15
Common stock, shares issued | shares									109,523,493	77,421,683
Common stock, par value (in usd per share)									$ 0.001	$ 0.001		$ 0.001
Preferred stock, shares issued | shares									72,885	73,335
Common stock, price per share (in usd per share)														$ 34.05
Allocated intrinsic value | $	$ 52,000,000													$ 40,900,000
Common stock, shares authorized | shares									300,000,000	150,000,000		300,000,000	150,000,000
Preferred stock, par value (in usd per share)									$ 0.001	$ 0.001
Consideration received on transaction, net of issuance costs | $		$ 0	$ 684,200,000
Aggregate common shares issued upon conversion | shares		12,128,115	12,128,115
Equity issuance, per share amount (in usd per share)				$ 25.00			$ 22.75
Proceeds from issuance of common stock | $				$ 413,200,000			$ 239,500,000		$ 1,260,000,000	$ 1,131,300,000	$ 253,600,000
Class of warrant or right, exercise price of warrants or rights (in dollars per share)								$ 7.00
Class of warrant or right, number of securities called by warrants or rights | shares									10,462,455
Common Stock
Stockholders Equity [Line Items]
Stock issued during period, new issues | shares					15,000,000		9,694,027		15,499,000	27,953,000	11,148,000
Shares issued and sold as a result of the full exercise of the underwriters' over-allotment option | shares				2,250,000		1,454,104
Purchased Common Shares
Stockholders Equity [Line Items]
Common stock, shares issued | shares	15,499,445		10,702,934
Common stock, par value (in usd per share)	$ 0.001
Preferred stock, shares issued | shares			371,848
Shares issued, price per share (in usd per share)	$ 45.00		$ 30.66
Proceeds from issuance of private placement | $	$ 697,500,000		$ 328,000,000
Common stock, price per share (in usd per share)	$ 49.16
Series C Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, shares issued | shares	562,525
Shares issued, price per share (in usd per share)	$ 1,000
Proceeds from issuance of private placement | $	$ 562,500,000
Proceeds from issuance of restricted stock, net of issuance costs | $	$ 1,228,100,000
Number of shares issued upon conversion | shares	12,500,546
Conversion price (in usd per share)	$ 45.00
Purchased Preferred Stock
Stockholders Equity [Line Items]
Shares issued, price per share (in usd per share)			$ 1,000
Proceeds from issuance of private placement | $			$ 372,000,000
Conversion price (in usd per share)			$ 30.66
Preferred stock, par value (in usd per share)			$ 0.001
Discount rate (as a percent)			5.00%
Trailing trading days			20 days
Convertible Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, par value (in usd per share)								$ 0.001
Proceeds from Issuance of Preferred Stock and Preference Stock | $								$ 75,000,000
Proceeds from issuance of preferred stock, net of issuance costs (in shares) | shares								75,000
Temporary equity, liquidation preference | $								$ 1,000
Class of warrant or right, exercise price of warrants or rights (in dollars per share)								$ 7.00
Class of warrant or right, number of securities called by warrants or rights | shares									10,412,145
Preferred stock, liquidation preference, percentage								4.00%