Convertible Senior Notes (Parenthetical) (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2014	Jul. 31, 2013
4.25% Convertible Senior Notes (due 2018)
Debt Instrument [Line Items]
Debt instrument, maturity year	2018	2018
Debt instrument, interest rate	4.25%	4.25%		4.25%
4.875% Convertible Senior Notes (due 2020)
Debt Instrument [Line Items]
Debt instrument, maturity year	2020	2020
Debt instrument, interest rate	4.875%	4.875%	4.875%