Debt - Encore Convertible Notes (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)	Mar. 05, 2014 $ / shares	Jul. 31, 2013 USD ($)	Jun. 24, 2013 $ / shares	Dec. 31, 2012 USD ($)	Nov. 27, 2012 $ / shares
Debt Instrument [Line Items]
Convertible senior notes sold	$ 448,500,000	$ 448,500,000
Equity component	58,184,000	55,236,000
Liability component—principal amount	448,500,000	448,500,000
Unamortized debt discount	(41,867,000)	(51,202,000)
Liability component—net carrying amount	406,633,000	397,298,000
Convertible Notes [Member]
Debt Instrument [Line Items]
Interest expense—stated coupon rate	13,245,000	12,418,000
Interest expense—amortization of debt discount	9,335,000	8,423,000
Total interest expense	$ 22,580,000	$ 20,841,000
2017 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Initial conversion price (in dollars per share) | $ / shares	$ 31.56							$ 31.56
Closing stock price at date of issuance (in dollars per share) | $ / shares	$ 25.66
Conversion rate (in shares per $1,000 principal amount)	31.6832
Debt component	$ 100,298,000
Equity component	14,702,000
Equity issuance cost	$ 788,000
Stated interest rate	3.00%
Effective interest rate	6.00%
2017 Convertible Senior Notes [Member] | Convertible Notes [Member]
Debt Instrument [Line Items]
Convertible senior notes sold							$ 115,000,000.0
Stated interest rate							3.00%
2020 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Initial conversion price (in dollars per share) | $ / shares	$ 45.72					$ 45.72
Closing stock price at date of issuance (in dollars per share) | $ / shares	$ 33.35
Conversion rate (in shares per $1,000 principal amount)	21.8718
Debt component	$ 140,247,000
Equity component	32,253,000
Equity issuance cost	$ 1,106,000
Stated interest rate	3.00%
Effective interest rate	6.35%
2020 Convertible Senior Notes [Member] | Convertible Notes [Member]
Debt Instrument [Line Items]
Convertible senior notes sold					$ 172,500,000
Stated interest rate					3.00%
2021 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Initial conversion price (in dollars per share) | $ / shares	$ 59.39			$ 59.39
Closing stock price at date of issuance (in dollars per share) | $ / shares	$ 47.51
Conversion rate (in shares per $1,000 principal amount)	16.8386
Debt component	$ 143,645,000
Equity component	17,355,000
Equity issuance cost	$ 581,000
Stated interest rate	2.875%
Effective interest rate	4.70%
2021 Convertible Senior Notes [Member] | Convertible Notes [Member]
Debt Instrument [Line Items]
Convertible senior notes sold			$ 161,000,000.0
Stated interest rate			2.875%