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Net Income per Share (Narrative) (Detail) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Mar. 31, 2018	Nov. 22, 2016	Nov. 20, 2015	Feb. 12, 2014
Restricted Stock [Member]
Debt Instrument [Line Items]
Antidilutive securities excluded from computation of earnings per share (in Shares)	1.1	1.0	0.0	1.1
Option on Securities [Member]
Debt Instrument [Line Items]
Antidilutive securities excluded from computation of earnings per share (in Shares)	12.7	4.9	0.0	4.9
February 2018 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						4.00%
Convertible notes									$ 300,000
December 2021 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.75%		2.75%				2.75%
Convertible notes	$ 128,520		$ 128,520		$ 124,644		$ 150,000	$ 150,000