Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Tax Examination [Line Items]
Valuation allowance	$ 4,200,000		$ 4,200,000
Effective tax rate			37.60%	1.00%
Income tax expense	9,220,000	96,000	16,547,000	293,000
Excess tax benefits from stock-based awards			$ 12,500,000
Earliest Tax Year [Member] | State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Years subject to income tax examination			2008
Earliest Tax Year [Member] | Michigan [Member]
Income Tax Examination [Line Items]
Tax examination year under examination	2008
Earliest Tax Year [Member] | Federal Tax Jurisdiction [Member]
Income Tax Examination [Line Items]
Years subject to income tax examination			2010
Latest Tax Year [Member] | State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Years subject to income tax examination			2013
Latest Tax Year [Member] | Michigan [Member]
Income Tax Examination [Line Items]
Tax examination year under examination	2011
Latest Tax Year [Member] | Federal Tax Jurisdiction [Member]
Income Tax Examination [Line Items]
Years subject to income tax examination			2013