Related Party Transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related party transactions
Future minimum lease commitments relating to leases	$ 4,967,678,000
Affiliates of Entity Chairman
Related party transactions
Rent expense	1,100,000	1,100,000	1,000,000
Future minimum lease commitments relating to leases	$ 5,200,000