Debt and Financing Arrangements - Summary of Recognized Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total interest expense	$ 1,689	$ 1,777	$ 1,692	$ 1,517	$ 1,574	$ 1,760	$ 1,733	$ 1,526	$ 6,675	$ 6,593	$ 8,902
2010 Convertible Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Total interest expense											4,559
Credit Facility [Member]
Debt Instrument [Line Items]
Total interest expense									$ 6,675	6,585	4,320
2006 Convertible Senior Subordinated Notes [Member]
Debt Instrument [Line Items]
Total interest expense										$ 8	$ 23