Debt Outstanding Excluding Lease Obligations (Detail) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Debt Instrument [Line Items]
Principal Balance	$ 810,952		$ 695,748
Unamortized Discount and Debt Issuance Costs	24,194		28,150
Net Carrying Amount	786,758		667,598
Principal Balance, Current	20,952		20,538
Unamortized Discount and Debt Issuance Costs, Current	434		479
Net Carrying Amount, Current	20,518		20,059
Principal Balance, Noncurrent	790,000		675,210
Unamortized Discount and Debt Issuance Costs, Noncurrent	23,760		27,671
Net Carrying Amount, Noncurrent	766,240		647,539
1.25% Cash Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Principal Balance	345,000	[1]	345,000
Unamortized Discount and Debt Issuance Costs	18,534		22,112
Net Carrying Amount	326,466		322,888
Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Principal Balance	465,000		350,000
Unamortized Discount and Debt Issuance Costs	5,660		6,038
Net Carrying Amount	459,340		343,962
Other Debt [Member]
Debt Instrument [Line Items]
Principal Balance	952		748
Unamortized Discount and Debt Issuance Costs	0		0
Net Carrying Amount	$ 952		$ 748

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