Business Combinations (Narrative) (Details) - USD ($)		1 Months Ended	2 Months Ended	3 Months Ended												12 Months Ended
	Dec. 08, 2020	Dec. 31, 2020	Feb. 17, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Revenue				$ 383,413,000	$ 331,542,000	$ 389,050,000	$ 273,255,000	$ 332,194,000	$ 289,796,000	$ 393,222,000	$ 303,429,000	$ 355,972,000	$ 245,346,000	$ 308,530,000	$ 260,178,000	$ 1,377,260,000	$ 1,318,641,000	$ 1,170,026,000
Net income				$ 48,919,000	$ 45,490,000	$ 53,120,000	$ 22,829,000	$ 51,565,000	$ 25,272,000	$ 54,131,000	$ 18,172,000	$ 35,460,000	$ 23,112,000	$ 45,727,000	$ 17,207,000	170,358,000	149,140,000	121,506,000
Acquisition-related costs																6,014,000	$ 777,000	$ 5,093,000
Common stock consideration fair value																1,459,000
Rouse Services LLC [Member]
Business Acquisition [Line Items]
Total consideration	$ 251,724,000
Cash consideration	250,265,000
Cash consideration, placed in escrow	$ 2,169,000
Maximum period to identify and measure the assets acquired and liabilities assumed	1 year
Revenue		$ 1,922,000
Net income		181,000
Amortization of intangible assets		$ 460,000
Common stock consideration (in shares)	312,193
Vesting period	3 years
Acquisition-related costs																6,014,000
Common stock consideration fair value	$ 1,459,000
Acquisition-related costs for legal, advisory, integration and other professional fees																6,014,000
Acquisition related share based continuing employment costs																802,000
Rouse Services LLC [Member] | Employment Costs [Member]
Business Acquisition [Line Items]
Acquisition-related costs																802,000
Common stock consideration fair value	$ 20,735,000
Rouse Services LLC [Member] | Other Related Costs [Member]
Business Acquisition [Line Items]
Acquisition-related costs																$ 5,212,000
Subsequent Events [Member] | Rouse Services LLC [Member]
Business Acquisition [Line Items]
Common stock consideration (in shares)			256,683
Common stock consideration fair value			$ 17,931,000
Shares forfeited			55,510