Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Amount charged to affiliate for aircraft use	$ 17,600	$ 12,900	$ 19,400
Amount charged to company by affiliate for aircraft use	303,000	598,000	460,000
Officers And Other Key Employees [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party	300,000	200,000	300,000
Due to affiliates	35,000	41,000
Revenues paid to related party	400,000	500,000	500,000
Due from affiliates	127,000	67,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Total amount paid to related party	426,000	529,000	368,000
Due to affiliates	38,000	161,000
Due from affiliates	1,400	2,700
Total amount received from related party	$ 18,900	$ 14,400	$ 18,600