Long-Term Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Dec. 31, 2017	Jan. 31, 2015	Apr. 30, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Long-Term Incentive Plan
Amortization related to shares issued to design and construction employees				$ 472	$ 591	$ 580
Restricted Shares
Long-Term Incentive Plan
Number of common shares reserved for issuance under LTIP (in shares)	12,050,000			12,050,000
Number of shares available for future issuance (in shares)	4,824,586			4,824,586
Amortization Expense, including forfeitures				$ 8,042	7,157	9,695
Amortization related to shares issued to design and construction employees				$ 500	$ 600	$ 600
Non-vested stock grants, number of shares
Outstanding at the beginning of the period (in shares)		1,883,296		1,095,908	986,345	1,883,296
Granted (in shares)				654,266	816,880	499,787
Vested (in shares)				(541,827)	(605,641)	(1,225,443)
Forfeited (in shares)				(33,298)	(101,676)	(171,295)
Outstanding at the end of the period (in shares)	1,175,049			1,175,049	1,095,908	986,345
Non-vested stock grants, weighted average price
Outstanding at the beginning of the period (in dollars per share)		$ 11.24		$ 13.36	$ 14.33	$ 11.24
Granted (in dollars per share)				15.11	12.33	17.33
Vested (in dollars per share)				13.78	13.39	10.75
Forfeited (in dollars per share)				14.10	14.32	14.76
Outstanding at the end of the period (in dollars per share)	$ 14.12			$ 14.12	$ 13.36	$ 14.33
Restricted Shares | Minimum
Long-Term Incentive Plan
Vesting period				3 years
Restricted Shares | Maximum
Long-Term Incentive Plan
Vesting period				5 years
Restricted Shares | Former Chief Executive Officer
Long-Term Incentive Plan
Amortization Expense, including forfeitures		$ 2,500
Stock Options | Former Chairman
Stock options
Number of options granted (in shares)			200,000
Exercise price of outstanding options (in dollars per share)			$ 17.71
Expiration date of outstanding options	Apr. 27, 2018
Deferred shares, share purchase rights, or share appreciation rights issued or outstanding under the LTIP
Non-vested stock grants, number of shares
Outstanding at the end of the period (in shares)	0			0