Long-Term Debt - Notes Payable to BMI - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Cash Collateral		$ 24,200,000	$ 19,600,000
Repayment of note payable		309,000,000	$ 53,400,000	$ 343,100,000
BMI | Bank note payable
Debt Instrument [Line Items]
Note payable, secured					$ 11,900,000
Cash Collateral					$ 750,000
Periodic principal payments		$ 100,000
Loans maturity period		Jan. 31, 2025
Frequency of debt instrument payment		Monthly
Interest rate terms		The note bears interest at a variable rate equal to the prime rate with a floor of 3.25% and a ceiling of 9.0
Debt instrument, average interest rate during period		3.50%
Notes payable outstanding		$ 8,500,000
Debt instrument, Effective interest rate at period end		3.75%
Debt issuance cost		$ 100,000
BMI | Bank note payable | Subsequent Event
Debt Instrument [Line Items]
Repayment of note payable	$ 8,500,000
BMI | Bank note payable | 2017 Bank Loan | Subsequent Event
Debt Instrument [Line Items]
Frequency of debt instrument payment	semi-annual
Debt issuance cost	$ 1,000,000
Principal amount of loan agreement	$ 20,500,000
Debt instrument, payment terms	The agreement requires semi-annual payments of principal and interest on June 1 and December 1 aggregating $1.9 million annually beginning on June 1, 2017 through the maturity date in June 2032 (except during 2017 which calls for prorated aggregate principal and interest payments of $1.6 million).
Periodic principal and interest payments	$ 1,900,000
Loans maturity period	2032-06
Prorated principal and interest payments	$ 1,600,000
Interest rate	5.34%
BMI | Bank note payable | Maximum
Debt Instrument [Line Items]
Debt instrument, average interest rate during period		9.00%
BMI | Bank note payable | Minimum
Debt Instrument [Line Items]
Debt instrument, average interest rate during period		3.25%