Summary of Financial Statement Affected by Application of ASU 2014-09 and Related Amendments (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	$ 263,779	$ 243,378	$ 525,668	$ 492,645
Income tax expense	3,083	2,371	6,119	9,603
Net income	$ 16,659	$ 8,513	$ 29,625	$ 33,915
Basic earnings per share	$ 0.46	$ 0.23	$ 0.81	$ 0.92
Diluted earnings per share	$ 0.45	$ 0.23	$ 0.81	$ 0.92
Balance Sheet June 30, 2018
Accounts receivable, net of allowance for doubtful accounts	$ 200,024		$ 200,024		$ 185,058
Accrued liabilities	72,781		72,781		77,209
Unearned revenue	5,768		5,768		4,889
Deferred income taxes, net	77,126		77,126
Accumulated earnings	351,691		351,691		$ 293,645
Revenue Based on Previously Effective Guidance
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	263,058		524,267
Income tax expense	3,232		6,409
Net income	$ 16,087		$ 28,514
Basic earnings per share	$ 0.44		$ 0.78
Diluted earnings per share	$ 0.44		$ 0.78
Balance Sheet June 30, 2018
Accounts receivable, net of allowance for doubtful accounts	$ 200,024		$ 200,024
Accrued liabilities	70,100		70,100
Unearned revenue	3,087		3,087
Deferred income taxes, net	76,578		76,578
Accumulated earnings	353,824		353,824
ASU 2014-09 | New Revenue Standard Adjustment
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Product revenues	721		1,401
Income tax expense	(149)		(290)
Net income	$ 572		$ 1,111
Basic earnings per share	$ 0.02		$ 0.03
Diluted earnings per share	$ 0.02		$ 0.03
Balance Sheet June 30, 2018
Accrued liabilities	$ 2,681		$ 2,681
Unearned revenue	2,681		2,681
Deferred income taxes, net	548		548
Accumulated earnings	$ (2,133)		$ (2,133)