Earnings Per Share (Details) (USD $)	3 Months Ended	9 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Earnings for basic computations	$ 52,010,000us-gaap_UndistributedEarnings	$ 45,689,000us-gaap_UndistributedEarnings	$ 186,275,000us-gaap_UndistributedEarnings	$ 183,605,000us-gaap_UndistributedEarnings
Weighted-average common shares outstanding for basic computations	146,664,977	142,864,060	145,279,406	140,671,170
Earnings for diluted computations	52,025,000us-gaap_UndistributedEarningsDiluted	45,689,000us-gaap_UndistributedEarningsDiluted	186,275,000us-gaap_UndistributedEarningsDiluted	183,605,000us-gaap_UndistributedEarningsDiluted
Dilutive stock options and restricted stock	4,014,108	5,971,223	4,960,430	7,494,020
Average number of common shares outstanding for diluted computations	150,679,085	148,835,283	150,239,836	148,165,190
Earnings per common share, Basic	$ 0.35us-gaap_EarningsPerShareBasic	$ 0.32us-gaap_EarningsPerShareBasic	$ 1.28us-gaap_EarningsPerShareBasic	$ 1.31us-gaap_EarningsPerShareBasic
Earnings per common share, Diluted	$ 0.35us-gaap_EarningsPerShareDiluted	$ 0.31us-gaap_EarningsPerShareDiluted	$ 1.24us-gaap_EarningsPerShareDiluted	$ 1.24us-gaap_EarningsPerShareDiluted
Unvested shares, cash dividends paid			47,006,000us-gaap_PaymentsOfCapitalDistribution	52,065,000us-gaap_PaymentsOfCapitalDistribution
Restricted stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Unvested shares participating in the payment of the Company's dividends declared	2,200,000	1,300,000	2,200,000	1,300,000
Unvested shares, cash dividends paid	300,000	1,500,000	2,900,000	1,700,000
Undistributed earnings allocated to participating securities, basic	550,000	0	0	0
Undistributed earnings allocated to participating securities, diluted	$ 540,000	$ 0	$ 0	$ 0
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive options excluded from the computation of EPS	100,000	101,000	302,000	104,000
Common stock, Class A
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average common shares outstanding for basic computations	146,664,977	140,948,396	144,482,223	138,540,878
Non-voting common stock, Class B
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average common shares outstanding for basic computations	0	947,259	293,071	1,087,755
Restricted common stock, Class C
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average common shares outstanding for basic computations	0	968,405	504,112	1,042,537

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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Cash outflow to owners or shareholders, excluding ordinary dividends. Includes special dividends.

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The earnings that is allocated to common stock and participating securities to the extent that each security may share in earnings as if all of the earnings for the period had been distributed.

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