Long-Term Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2008	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Long-Term Incentive Plan
Amortization related to shares issued to design and construction employees				$ 309	$ 486
Restricted Shares
Long-Term Incentive Plan
Amortization Expense, including forfeitures		$ 2,591	$ 2,463	4,340	4,077
Amortization related to shares issued to design and construction employees		$ 200	$ 200	$ 300	$ 500
Restricted Shares | Minimum
Long-Term Incentive Plan
Vesting period				3 years
Restricted Shares | Maximum
Long-Term Incentive Plan
Vesting period				5 years
Stock Options | Former Chairman
Stock options
Number of nonqualified stock options approved by the compensation committee of the Company's board of directors (in shares)	200,000
Exercise price of outstanding options (in dollars per share)		$ 17.71		$ 17.71
Expiration date of outstanding options	Apr. 27, 2018