Balance Sheet Information - Summary of Changes in Product Recall Liability (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Regulatory Assets [Abstract]
Beginning balance	$ 1,888us-gaap_AccruedMarketingCostsCurrent
Accrual for recall costs	505htwr_AccrualForRecallCosts	0htwr_AccrualForRecallCosts
Recall costs incurred during the period	(1,305)us-gaap_InventoryRecallExpense
Ending balance	$ 1,088us-gaap_AccruedMarketingCostsCurrent

Carrying value as of the balance sheet date of obligations incurred through that date and payable for the marketing, trade and selling of the entity's goods and services. Marketing costs would include expenditures for planning and executing the conception, pricing, promotion, and distribution of ideas, goods, and services; costs of public relations and corporate promotions; and obligations incurred and payable for sales discounts, rebates, price protection programs, etc. offered to customers and under government programs. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

No definition available.

Name:	us-gaap_AccruedMarketingCostsCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant