Fair Value of Financial Instruments - Other Investments - Other Equity Method Investments - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity in earnings (losses)	$ 8,714,000		$ 7,445,000	$ 23,585,000	$ 22,092,000
Equity method investments, net investment	250,000,000			250,000,000		$ 220,000,000
Confluence
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, ownership percentage		75.00%
Equity method investments, equity contributions	300,000			1,300,000
Equity method investments, equity in earnings (losses)	(200,000)			(600,000)
Confluence | Maximum
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Financing commitments		$ 2,500,000
Telecommunications Equity Method Investees
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, equity contributions	0			2,000,000
Equity method investments, equity in earnings (losses)	1,000,000				(1,000,000)
Equity method investments, net investment	20,000,000			20,000,000		19,000,000
Payments for advance to affiliate	0			200,000
Telecommunications Equity Method Investees | Subcontracting Arrangements
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Expenses, related party	3,200,000		2,700,000	7,300,000	9,000,000
Payables, related party	200,000			200,000		200,000
Telecommunications Equity Method Investees | Employee Leasing Arrangement
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Expenses, related party			$ 100,000		$ 300,000
Receivables, related party	$ 500,000			$ 500,000		400,000
FM Tech
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Equity method investments, ownership percentage	50.00%			50.00%
Equity method investments, equity contributions		$ 2,000,000
Equity method investments, net investment	$ 17,000,000			$ 17,000,000		16,000,000
FM Tech | Equity Method Investments
Fair Value, Financial Instruments Measured on a Non-Recurring Basis [Line Items]
Financing commitments	$ 3,000,000			$ 3,000,000		$ 9,000,000