Debt and Financing Arrangements - Summary of Recognized Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total interest expense	$ 1,434	$ 1,614	$ 1,817	$ 1,780	$ 1,689	$ 1,777	$ 1,692	$ 1,517	$ 6,645	$ 6,675	$ 6,593
2006 Convertible Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Total interest expense											8
Credit Facility [Member]
Debt Instrument [Line Items]
Total interest expense									$ 6,645	$ 6,675	$ 6,585