Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Revenues from transactions with related party	$ 0	$ 0	$ 1,400,000
Production expenses to affiliates	0	0	1,654,000
Total amount paid to related party		100,000	7,700,000
Amount charged to affiliate for aircraft use	19,400	9,500	9,600
Amount charged to company by affiliate for aircraft use	460,000	292,000	236,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Expenses from transactions with related party			8,800,000
Capitalized costs		100,000	2,600,000
Production expenses to affiliates			1,700,000
Total amount paid to related party			9,200,000
Officers And Other Key Employees [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party	300,000	300,000	500,000
Due to affiliates	48,000	45,000
Revenues paid to related party	500,000	400,000	700,000
Due from affiliates	58,000	90,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Total amount paid to related party	368,000	195,000	221,000
Due to affiliates	92,000	97,000
Due from affiliates	4,200	3,400
Total amount received from related party	$ 18,600	$ 6,800	33,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party			$ 1,400,000