Long-Term Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Jan. 31, 2015	Apr. 30, 2008	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Long-Term Incentive Plan
Amortization related to shares issued to design and construction employees					$ 304	$ 234
Vesting of restricted stock presented on statement of equity					716
Amortization of deferred stock compensation					4,681	3,316
Restricted Shares and Performance awards
Long-Term Incentive Plan
Compensation Expense, including forfeitures			$ 2,412	$ 2,671	6,844	$ 4,707
Net-settle adjustment					(6,432)
Amortization related to shares issued to design and construction employees					304
Vesting of restricted stock presented on statement of equity					$ 716
Restricted Shares and Performance awards | Minimum
Long-Term Incentive Plan
Vesting period					3 years
Restricted Shares and Performance awards | Maximum
Long-Term Incentive Plan
Vesting period					5 years
Restricted Shares and Performance awards | Kenneth E. Cruse
Long-Term Incentive Plan
Compensation Expense, including forfeitures	$ 2,500
Amortization of deferred stock compensation	$ 1,600
Stock Options | Robert A. Alter
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 options vested (in dollars per share)		$ 17.71	$ 17.71		$ 17.71