Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 1,522,300	$ 1,061,000
Long-term Debt, Current Maturities	(459,201)	0
Long-term debt	1,063,090	1,060,955
1 3⁄4% Senior Convertible Notes due 2017
Debt Instrument [Line Items]
Long-term debt	283,500	279,300
Long-term Debt, Current Maturities	(283,500)
7 1⁄2% Senior Notes due 2022
Debt Instrument [Line Items]
Long-term debt	770,200	770,000
Revolving credit facility
Debt Instrument [Line Items]
Long-term debt	457,000	0
Long-term Debt, Current Maturities	(175,300)
4.20% Building Loan
Debt Instrument [Line Items]
Long-term debt	11,600	$ 11,700
Long-term Debt, Current Maturities	$ (400)