Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended			1 Months Ended	0 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Apr. 30, 2014	Apr. 01, 2015	Aug. 12, 2014
Stockholders Equity [Line Items]
Common stock, shares issued	90,204,351	90,191,100
Unvested shares of common stock	4,045,960
Number of shares repurchased	4,105,970	4,105,970
Secondary offering costs			$ 674,000
Share Repurchase Program, authorized amount						250,000,000
Shares repurchased	0	855,970
Stock repurchase during period under Share Repurchase Program, average price per share		$ 17.50
Share Repurchase Program, remaining authorized repurchase amount		235,000,000
Stock repurchased during period, total cost		15,000,000
Shares repurchased payment settlement during period	5,650,000
Treasury stock at cost	109,871,000	109,871,000
Dividends paid to common stockholders	18,098,000		17,691,000
Dividends payable	18,373,000	172,000
Dividends payable on unvested restricted performance shares probable of vesting	18,373,000		18,015,000
Secondary Offering [Member]
Stockholders Equity [Line Items]
Common stock, shares issued				0
Number of shares repurchased				1,750,000
Shares offered and sold by the selling stockholders				17,250,000
Treasury stock at cost	109,871,000	109,871,000
Subsequent Event [Member]
Stockholders Equity [Line Items]
Dividends paid					18,100,000
2.25x Performance Restricted Shares [Member]
Stockholders Equity [Line Items]
Unvested shares of common stock	1,438,569	1,451,453
Dividends payable on unvested restricted performance shares not probable of vesting	2,360,000
2.75x Performance Restricted Shares [Member]
Stockholders Equity [Line Items]
Unvested shares of common stock	1,438,569	1,451,453
Dividends payable on unvested restricted performance shares not probable of vesting	2,360,000
Bonus Performance Restricted Shares [Member]
Stockholders Equity [Line Items]
Unvested shares of common stock	420,004
Dividends payable on unvested restricted performance shares not probable of vesting	88,000
Long-Term Incentive Performance Restricted Shares [Member]
Stockholders Equity [Line Items]
Unvested shares of common stock	75,832
Dividends payable on unvested restricted performance shares not probable of vesting	30,000
Dividends payable on unvested restricted shares, maximum	50,000
Long-Term Incentive Performance Restricted Shares [Member] | Target Performance [Member]
Stockholders Equity [Line Items]
Dividends payable on unvested restricted performance shares probable of vesting	$ 20,000