Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Parenthetical) (Details)	Dec. 31, 2015	Dec. 31, 2014
2.875% Senior notes due October 1, 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	2.875%	2.875%
2.875% Senior notes due October 1, 2022 | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	2.875%	2.875%
3.35% Senior notes due December 15, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	3.35%	3.35%
3.35% Senior notes due December 15, 2015 | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	3.35%	3.35%
2.45% Senior notes due December 15, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	2.45%	2.45%
2.45% Senior notes due December 15, 2019 | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate of debt	2.45%	2.45%