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Common Equity and Earnings Per Share - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Class of Stock
Payments of dividends, common stock	$ 0us-gaap_PaymentsOfDividendsCommonStock	$ 0us-gaap_PaymentsOfDividendsCommonStock
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
2013 Plan
Class of Stock
Shares issuable under stock options excluded from calculation of diluted earnings per share	285,000
Class A
Class of Stock
Common stock, votes per share	One
Class A \| 2013 Plan
Class of Stock
Shares issuable under stock options excluded from calculation of diluted earnings per share			600,000
Class B Convertible
Class of Stock
Common stock, votes per share	Ten