Common Stock and Treasury Stock (Details Textual) (Class A Common Stock [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014
Class A Common Stock [Member]
Common Stock [Line Items]
Share repurchase program, authorized amount	$ 75.8
Stock repurchase program, remaining authorization amount	$ 29.9

Amount remaining of a stock repurchase plan authorized by an entity's Board of Directors.

No definition available.

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration