Summary of Future Debt Payment Obligations (Detail) - USD ($) $ in Thousands		Mar. 31, 2019		Dec. 31, 2018
Debt Instrument [Line Items]
Total		$ 810,952		$ 695,748
Remainder of 2019		15,952
2020		372,500
2021		30,000
2022		37,500
2023		355,000
Thereafter		0
1.25% Cash Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Total		345,000	[1]	345,000
Remainder of 2019	[1]	0
2020	[1]	345,000
2021	[1]	0
2022	[1]	0
2023	[1]	0
Thereafter	[1]	0
Senior Secured Term Loan [Member]
Debt Instrument [Line Items]
Total		345,000
Remainder of 2019		15,000
2020		27,500
2021		30,000
2022		37,500
2023		235,000
Thereafter		0
Other Debt [Member]
Debt Instrument [Line Items]
Total		952		$ 748
Remainder of 2019		952
2020		0
2021		0
2022		0
2023		0
Thereafter		0
Revolving Facility [Member]
Debt Instrument [Line Items]
Total	[2]	120,000
Remainder of 2019	[2]	0
2020	[2]	0
2021	[2]	0
2022	[2]	0
2023	[2]	120,000
Thereafter	[2]	$ 0

[1] Assumes no cash conversions of the 1.25% Notes prior to their maturity on July 1, 2020.

[2] Assumes no additional borrowings after March 31, 2019, payment of any required periodic installments of principal and that all drawn amounts are repaid upon maturity.