Cover page. Cover page. Class A Common Common Class A [Member] Entities [Table] Entities [Table] Security Exchange Name Security Exchange Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Registrant Name Entity Registrant Name Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Entity Address, Address Line One Entity Address, Address Line One Local Phone Number Local Phone Number Written Communications Written Communications Soliciting Material Soliciting Material Trading Symbol Trading Symbol Entity Address, State or Province Entity Address, State or Province Pre-commencement Tender Offer Pre-commencement Tender Offer Amendment Flag Amendment Flag Document Period End Date Document Period End Date Class B Common Common Class B [Member] Document Type Document Type City Area Code City Area Code Class of Stock [Domain] Class of Stock [Domain] Entity Emerging Growth Company Entity Emerging Growth Company Entity File Number Entity File Number Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, City or Town Entity Address, City or Town Entity Central Index Key Entity Central Index Key Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] NASDAQ Global Market NASDAQ/NMS (GLOBAL MARKET) [Member] Entity Information [Line Items] Entity Information [Line Items] Exchange [Domain] Exchange [Domain] Title of 12(b) Security Title of 12(b) Security Class of Stock [Axis] Class of Stock [Axis]