Liquidity - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jul. 31, 2013	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents		$ 46,779	$ 64,977	$ 68,032	$ 86,064
Convertible senior notes, principal\ fair value amount		157,668	156,647
4.25% Convertible Senior Notes (due 2018)
Cash and Cash Equivalents [Line Items]
Convertible senior notes, principal\ fair value amount	$ 100,000	$ 21,178	21,178
Line of credit facility, maturity date	Aug. 01, 2018	Jun. 15, 2018
Foreign Subsidiaries
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents		$ 39,700	$ 52,800