Stockholder's Equity - Shares of Common Stock Issued Under Employee Stock Purchase Plan (Details) - $ / shares	3 Months Ended
Jun. 30, 2019	Mar. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Number of shares available, beginning balance (in shares)		152,344
Shares issued during period (in shares)	4,301	5,357
Number of shares available, ending balance (in shares)	142,686
Per share price of shares issued during period (in dollars per share)	$ 105.36	$ 89.19

Number of shares issued during the period as a result of an employee stock purchase plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section S99
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration