Line of Credit - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Maximum ratio of total liabilities to tangible net worth	2.50
Line of Credit
Debt Instrument [Line Items]
Available borrowing under letter of credit	$ 45,600,000
Line of credit facility, increase (decrease), net	100,000,000.0
Line of credit borrowings	0	$ 0
Letters of credit outstanding amount	$ 4,400,000
Company's leverage ratio	0.001
Unsecured Revolving Line of Credit | Line of Credit
Debt Instrument [Line Items]
Total availability under line of credit agreement	$ 50,000,000.0
Letter of Credit | Line of Credit
Debt Instrument [Line Items]
Available borrowing under letter of credit	$ 10,000,000.0
Minimum | London Interbank Offered Rate (LIBOR) | Line of Credit
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	1.00%
Maximum | London Interbank Offered Rate (LIBOR) | Line of Credit
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	1.50%