Unaudited Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 77,183,441us-gaap_NetIncomeLoss	$ 68,566,071us-gaap_NetIncomeLoss
Other comprehensive income (loss) before tax:
Foreign currency translation adjustments	(942,974)	(91,250)
Unrealized gains (losses) on derivatives	(1,831,690)	0
Unrealized gains (losses) on available-for sales securities, net	(577,685)	(3,692,791)
Other comprehensive income (loss), before tax	(3,352,349)	(3,784,041)
Provision (Benefit) for income taxes related to components of other comprehensive income	(843,281)us-gaap_OtherComprehensiveIncomeLossTax	(1,292,477)us-gaap_OtherComprehensiveIncomeLossTax
Other comprehensive income (loss), net of tax	(2,509,068)	(2,491,564)
Comprehensive Income	$ 74,674,373us-gaap_ComprehensiveIncomeNetOfTax	$ 66,074,507us-gaap_ComprehensiveIncomeNetOfTax

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount after tax, before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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