Line of Credit (Detail)	3 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
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	$ 47,300,000
Line of credit facility, increase (decrease), net	100,000,000.0
Line of credit borrowings	0	$ 0
Letters of credit outstanding amount	$ 2,700,000
Company's leverage ratio	0.0003
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%