Income Taxes - Income Tax Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2012
Current income taxes
Federal	$ (572)		$ 35,459	$ 51,058	$ 50,911
State	(4)		6,861	6,252	6,482
Foreign	5,255		7,069	6,650	3,368
Total	4,679		49,389	63,960	60,761
Deferred income taxes
Federal	1,669		8,234	(2,580)	(6,083)
State	(1)		624	(209)	414
Foreign	(4,404)		1,112	(1,303)	12
Total	(2,736)		9,970	(4,092)	(5,657)
Income taxes
Income tax expense	1,943	1,503	59,359	59,868	55,104
Foreign income before taxes	(3,631)		95,850	60,851	51,409
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)		77,399	71,945	64,282
State income taxes, net of federal income tax benefit	90		3,564	4,435	3,562
Foreign rate differential	1,904		(25,535)	(16,399)	(12,908)
Unrecognized tax benefits	0		3,566	0	0
Other	209		365	(113)	168
Income tax expense	1,943	1,503	59,359	59,868	55,104
Deferred tax assets (liabilities), current:
Uniform capitalization adjustment to inventory	4,114		4,040	5,492
Bad debt and other reserves	9,901		8,984	10,655
State taxes	(1,739)		482	508
Prepaid expenses	(2,217)		(3,546)	(2,193)
Accrued bonus	2,093		4,120	5,071
Foreign currency hedge	305		434	348
Net operating loss carry forwards	9,414		0	0
Other	0		(448)	0
Total deferred tax assets, current	21,871		14,066	19,881
Deferred tax assets (liabilities), noncurrent:
Amortization and impairment of intangible assets	5,267		1,004	4,603
Depreciation of property and equipment	(4,833)		(6,148)	(6,034)
Share-based compensation	10,638		12,044	11,226
Foreign currency translation	382		720	667
Deferred rent	4,290		4,885	4,028
Acquisition costs	756		764	755
Other	128		1,327	0
Net operating loss carry forwards	434		421	506
Total deferred tax assets, noncurrent	17,062		15,017	15,751
Unallocated deferred tax assets	$ 38,933		$ 29,083	$ 35,632