Stockholders' Equity (Summary of Activity Related to Restricted Stock Units) (Detail)	6 Months Ended
	Jun. 30, 2015 shares
Restricted Stock Units (RSUs) [Member]
Unvested shares
Outstanding, shares at December 31, 2014	1,200,884
Granted	328,034
Forfeited	(19,145)
Vested and issued	(426,864)
Vested and unissued	(46,521)
Outstanding, shares at June 30, 2015	1,036,388
Performance Shares [Member]
Unvested shares
Outstanding, shares at December 31, 2014	54,723
Granted	238,690
Outstanding, shares at June 30, 2015	293,413