Supplementary Financial Data Supplementary Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Financial Data [Abstract]
Revenue	$ 367,964us-gaap_SalesRevenueNet	$ 330,767us-gaap_SalesRevenueNet	$ 281,608us-gaap_SalesRevenueNet	$ 234,841us-gaap_SalesRevenueNet	$ 336,307us-gaap_SalesRevenueNet	$ 275,195us-gaap_SalesRevenueNet	$ 234,553us-gaap_SalesRevenueNet	$ 190,727us-gaap_SalesRevenueNet	$ 1,215,180us-gaap_SalesRevenueNet	$ 1,036,782us-gaap_SalesRevenueNet	$ 761,905us-gaap_SalesRevenueNet
Gross margin	73,759us-gaap_GrossProfit	68,509us-gaap_GrossProfit	59,587us-gaap_GrossProfit	50,877us-gaap_GrossProfit	67,030us-gaap_GrossProfit	54,909us-gaap_GrossProfit	46,216us-gaap_GrossProfit	38,314us-gaap_GrossProfit
Net Income (Loss) Available to Common Stockholders	$ 9,767	$ 12,399	$ 12,335	$ 11,413	$ 13,043	$ 124,092	$ 6,045	$ 2,397	$ 45,914	$ 145,577	$ 13,347
Earnings Per Share, Basic	$ 0.40us-gaap_EarningsPerShareBasic	$ 0.51us-gaap_EarningsPerShareBasic	$ 0.50us-gaap_EarningsPerShareBasic	$ 0.47us-gaap_EarningsPerShareBasic	$ 0.54us-gaap_EarningsPerShareBasic	$ 5.09us-gaap_EarningsPerShareBasic	$ 0.25us-gaap_EarningsPerShareBasic	$ 0.11us-gaap_EarningsPerShareBasic	$ 1.88us-gaap_EarningsPerShareBasic	$ 6.11us-gaap_EarningsPerShareBasic	$ 0.68us-gaap_EarningsPerShareBasic
Earnings Per Share, Diluted	$ 0.36us-gaap_EarningsPerShareDiluted	$ 0.44us-gaap_EarningsPerShareDiluted	$ 0.44us-gaap_EarningsPerShareDiluted	$ 0.41us-gaap_EarningsPerShareDiluted	$ 0.48us-gaap_EarningsPerShareDiluted	$ 4.22us-gaap_EarningsPerShareDiluted	$ 0.25us-gaap_EarningsPerShareDiluted	$ 0.11us-gaap_EarningsPerShareDiluted	$ 1.65us-gaap_EarningsPerShareDiluted	$ 5.24us-gaap_EarningsPerShareDiluted	$ 0.67us-gaap_EarningsPerShareDiluted
Basic Weighted Average Shares Outstanding	24,489	24,474	24,470	24,417	24,358	24,358	24,271	22,273	24,463	23,822	19,651
Diluted Weighted Average Shares Outstanding	29,944	29,921	29,913	29,870	29,783	29,745	24,646	22,688	29,912	28,763	19,891

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

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