Subsequent Events	12 Months Ended
Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	(15) Subsequent Events On January 1, 2019, certain enhancements to the 401(k) Plan became effective, including amendments to the Company’s matching contributions and the vesting schedule for current and active participants. See Note 12, Employee Benefit Plan, to the consolidated financial statements for further information regarding the 401(k) Plan. During the period January 1, 2019 through February 11, 2019, the Company repurchased an aggregate of 314,774 shares of its class A common stock at an average price per share of $132.01 and an aggregate cost of $41.6 million pursuant to the 2005 Share Repurchase Program. See Note 11, Treasury Stock, to the consolidated financial statements for further information regarding the 2005 Share Repurchase Program.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI http://asc.fasb.org/topic&trid=2122774

Name:	us-gaap_SubsequentEventsTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration