Quarterly Summary of Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									6 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Mar. 31, 2014	Mar. 31, 2013	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013
Summarized unaudited quarterly financial data
Net sales	$ 378,635	$ 795,902	$ 486,855	$ 213,805	$ 340,637	$ 784,678	$ 480,273	$ 294,716	$ 263,760	$ 211,469	$ 1,875,197	$ 1,817,057	$ 1,556,618
Gross profit	154,942	391,017	214,113	86,596	152,324	415,139	223,873	$ 144,260	$ 123,559	86,772	$ 846,668	$ 878,108	$ 736,483
Net (loss) income	$ (23,706)	$ 156,921	$ 36,377	$ (47,327)	$ 1,406	$ 156,706	$ 40,730			$ (37,062)
Net income (loss) per share:
Basic (in dollars per share)	$ (0.73)	$ 4.85	$ 1.12	$ (1.43)	$ 0.04	$ 4.54	$ 1.18	$ (0.08)	$ 0.03	$ (1.07)	$ 3.76	$ 4.70	$ 4.23
Diluted (in dollars per share)	$ (0.73)	$ 4.78	$ 1.11	$ (1.43)	$ 0.04	$ 4.50	$ 1.17	$ (0.08)	$ 0.03	$ (1.07)	$ 3.70	$ 4.66	$ 4.18