Basis of Presentation - Reconciliation of BEPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Reconciliation of basic earnings per share ("EPS") to diluted EPS
Net income available to common stockholders	$ 28,214	$ 26,201	$ 51,335	$ 42,544	$ 47,190
Basic weighted-average shares outstanding (in shares)	47,634	48,399	47,634	48,353
Dilutive effect of potential common stock equivalents — stock options and restricted stock units (in shares)	286	206	288	180
Diluted weighted-average shares outstanding (in shares)	47,920	48,605	47,922	48,533
Earnings per common share:
Basic (in dollars per share)	$ 0.59	$ 0.54	$ 1.08	$ 0.88
Diluted (in dollars per share)	$ 0.59	$ 0.54	$ 1.07	$ 0.88
Potentially dilutive securities excluded from earnings per diluted share because their effect is anti-dilutive	0	0	0	0