Quarterly Operating Results (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Line Items]
Revenues	$ 164,520	$ 201,477	$ 153,744	$ 147,657	$ 153,622	$ 151,134	$ 177,614	$ 163,166	$ 667,398	$ 645,536	$ 625,705
Gross profit	48,519	62,759	39,333	42,384	45,638	50,150	64,253	63,464	192,995	223,505	261,715
Net income	$ 20,854	$ 30,148	$ 16,307	$ 17,577	$ 19,827	$ 23,898	$ 31,917	$ 30,291	$ 84,886	$ 105,933	$ 130,136
Earnings per share:
Basic	$ 0.90	$ 1.31	$ 0.71	$ 0.76	$ 0.86	$ 1.04	$ 1.38	$ 1.31	$ 3.67	$ 4.59	$ 5.62
Diluted	$ 0.90	$ 1.31	$ 0.71	$ 0.76	$ 0.86	$ 1.04	$ 1.38	$ 1.31	$ 3.67	$ 4.59	$ 5.62