Summary of Financial Statement Affected by Application of ASU 2014-09 and Related Amendments (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	$ 261,889	$ 249,267
Income tax expense	3,036	7,232
Net income	$ 12,966	$ 25,402
Basic earnings per share	$ 0.35	$ 0.69
Diluted earnings per share	$ 0.35	$ 0.69
Balance Sheet
Accounts receivable, net of allowance for doubtful accounts	$ 196,616		$ 185,058
Accrued liabilities	72,908		77,209
Unearned revenue	6,800		4,889	$ 4,889
Deferred income taxes, net	78,918
Accumulated earnings	335,032		$ 293,645
Revenue Based on Previously Effective Guidance
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	261,209
Income tax expense	3,177
Net income	$ 12,427
Basic earnings per share	$ 0.34
Diluted earnings per share	$ 0.34
Balance Sheet
Accounts receivable, net of allowance for doubtful accounts	$ 196,616
Accrued liabilities	69,482
Unearned revenue	3,374
Deferred income taxes, net	78,218
Accumulated earnings	337,758
ASU 2014-09 | New Revenue Standard Adjustment
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	680
Income tax expense	(141)
Net income	$ 539
Basic earnings per share	$ 0.01
Diluted earnings per share	$ 0.01
Balance Sheet
Accrued liabilities	$ 3,426
Unearned revenue	3,426
Deferred income taxes, net	700
Accumulated earnings	$ (2,726)