Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Apr. 13, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 1,411,200		$ 1,061,000
Long-term Debt, Current Maturities	(288,336)		0
Long-term debt	1,122,901		1,060,955
1 3⁄4% Senior Convertible Notes due 2017
Debt Instrument [Line Items]
Long-term debt	287,900		279,300
Long-term Debt, Current Maturities	(287,900)
7 1⁄2% Senior Notes due 2022
Debt Instrument [Line Items]
Long-term debt	770,300		770,000
Revolving credit facility
Debt Instrument [Line Items]
Long-term debt	341,500		0
Long-term Debt, Current Maturities		$ (175,300)
4.20% Building Loan
Debt Instrument [Line Items]
Long-term debt	11,500		$ 11,700
Long-term Debt, Current Maturities	$ (400)