Summary of Convertible Debt (Detail) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Convertible Notes, net of unamortized deferred offering costs		$ 0	$ 22,478	[1]
Convertible Notes, net of unamortized discount and deferred offering costs		676,205	660,761	[1]
Total convertible debt, net		676,205	683,239
Convertible Notes, fair value		863,062	956,933
Convertible Notes due 2017
Debt Instrument [Line Items]
Convertible Notes		0	22,503
Convertible debt, Unamortized deferred offering costs		0	(25)
Convertible Notes, net of unamortized deferred offering costs		0	22,478
Convertible Notes, fair value	[2]	0	90,977
Convertible Notes due 2018
Debt Instrument [Line Items]
Convertible Notes		374,980	374,980
Convertible debt, unamortized discount		(20,122)	(27,566)
Convertible debt, Unamortized deferred offering costs		(2,515)	(3,484)
Convertible Notes, net of unamortized discount and deferred offering costs		352,343	343,930
Convertible Notes, fair value	[2]	416,337	423,202
Convertible Notes due 2020
Debt Instrument [Line Items]
Convertible Notes		374,993	374,993
Convertible debt, unamortized discount		(46,854)	(53,239)
Convertible debt, Unamortized deferred offering costs		(4,277)	(4,923)
Convertible Notes, net of unamortized discount and deferred offering costs		323,862	316,831
Convertible Notes, fair value	[2]	$ 446,725	$ 442,754

[1] December 31, 2016 balances were derived from the audited Consolidated Financial Statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, filed with the Securities and Exchange Commission (the SEC) on February 27, 2017.

[2] The fair value of the Company’s fixed rate convertible debt is based on open market trades and is classified as Level 1 in the fair value hierarchy.