Income Taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013
Current income taxes
Federal	$ (572)		$ 11,971	$ 35,459	$ 51,058
State	(4)		2,443	6,861	6,252
Foreign	5,255		12,039	7,069	6,650
Total	4,679		26,453	49,389	63,960
Deferred income taxes
Federal	1,669		7,887	8,234	(2,580)
State	(1)		1,113	624	(209)
Foreign	(4,404)		(833)	1,112	(1,303)
Total	(2,736)		8,167	9,970	(4,092)
Income taxes
Income tax expense	1,943	$ 1,503	34,620	59,359	59,868
Foreign income before taxes	(3,631)		105,938	95,850	60,851
Actual income taxes differed from that obtained by applying the statutory federal income tax rate to income before income taxes
Computed expected income taxes	(260)		54,910	77,399	71,945
State income taxes, net of federal income tax benefit	90		1,298	3,564	4,435
Foreign rate differential	1,904		(28,233)	(25,535)	(16,399)
Unrecognized tax benefits	0		3,670	3,566	0
Foreign tax expense on diminution of operations	0		1,352	0	0
Other	209		1,623	365	(113)
Income tax expense	$ 1,943	$ 1,503	$ 34,620	$ 59,359	$ 59,868