Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value [Abstract]

Carrying Values and Fair Values of Debt Instruments

	Carrying Value at				Fair Value* at
	June 30,		December 31,		June 30,		December 31,
	2020		2019		2020		2019
4.64% Senior Notes due 2021	$	100,000	$	100,000	$	102,149	$	102,654
2.39% Senior Notes due 2021	$	150,000	$	150,000	$	150,867	$	149,823
3.09% Senior Notes due 2022	$	125,000	$	125,000	$	128,492	$	126,884
2.75% Senior Notes due 2023	$	200,000	$	200,000	$	205,250	$	201,121
3.24% Senior Notes due 2024	$	150,000	$	150,000	$	157,506	$	153,804
3.41% Senior Notes due 2025	$	375,000	$	375,000	$	401,598	$	389,127
3.03% Senior Notes due 2026	$	400,000	$	400,000	$	422,163	$	406,768
3.49% Senior Notes due 2027	$	250,000	$	250,000	$	269,925	$	259,789
4.25% Senior Notes due 2028	$	500,000	$	500,000	$	568,200	$	562,050
3.50% Senior Notes due 2029	$	500,000	$	500,000	$	558,800	$	533,500
2.60% Senior Notes due 2030	$	600,000	$	—	$	630,480	$	—
3.05% Senior Notes due 2050	$	500,000	$	—	$	502,700	$	—

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*Senior Notes are classified as Level 2 within the fair value hierarchy. Fair value is based on quotes of bonds with similar ratings in similar industries.