Summary of Significant Accounting Policies Supplemental Disclosures Related to Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental cash flow information
Total interest costs incurred	$ 54,510	$ 54,636	$ 53,736
Interest capitalized	1,070	628	1,488
Interest expense	53,440	54,008	52,248
Cash paid for interest, net of amounts capitalized	53,467	51,975	52,632
Cash paid for income taxes	844	971	462
Supplemental schedule of noncash investing and financing activities
Accounts payable and accrued liabilities for construction in progress	22,884	25,413	14,440
Accrued leasing commissions	555	3,345	5,229
Reduction to capital for prepaid equity financing costs	0	0	241
Building recorded in termination of ground lease	$ 0	$ 4,518	$ 0