Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Amount charged to affiliate for aircraft use	$ 12,900	$ 19,400	$ 9,500
Amount charged to company by affiliate for aircraft use	598,000	460,000	292,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Capitalized costs			100,000
Officers And Other Key Employees [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party	200,000	300,000	300,000
Due to affiliates	41,000	48,000
Revenues paid to related party	500,000	500,000	400,000
Due from affiliates	67,000	58,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Total amount paid to related party	529,000	368,000	195,000
Due to affiliates	161,000	92,000
Due from affiliates	2,700	4,200
Total amount received from related party	$ 14,400	$ 18,600	$ 7,000