Related Party Transactions (Details) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
	Apr. 18, 2014 item	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Chairman and Chief Executive Officer
Related party transactions
Number of separate lease agreements	2
Aggregate monthly payments under non-cancelable operating lease agreements	$ 200,000
Percentage increase per annum in monthly lease payments under non-cancelable operating lease agreements	3.00%
Lease expense		600,000	600,000	1,300,000	1,200,000
O&G
Related party transactions
Ownership percentage in joint venture				30.00%
Estimated total contract value		364,000,000		364,000,000
Expenses incurred with related party		$ 1,856,000	$ 1,792,000	$ 3,359,000	$ 3,182,000
Number of Company's shares of common stock held by related party joint venture partner (in shares)		500,000	600,000	500,000	600,000
Percentage of common stock held by related party		1.03%	1.25%	1.03%	1.25%