Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 260,895	$ 172,667	$ 191,998	$ 263,776	$ 150,540	$ 162,842	$ 237,509	$ 182,115	$ 889,336	$ 733,006	$ 750,592
Gross profit	71,745	57,552	60,554	67,696	47,927	46,849	58,670	45,894	257,547	199,340	178,612
Net earnings	$ 36,151	$ 29,357	$ 32,969	$ 34,976	$ 22,723	$ 23,824	$ 32,216	$ 20,770	$ 133,453	$ 99,533	$ 86,896
Net earnings per common share—basic and diluted (in dollars per share)	$ 1.82	$ 1.39	$ 1.54	$ 1.64	$ 1.06	$ 1.12	$ 1.51	$ 0.97	$ 6.39	$ 4.66	$ 4.07